Karena stempel itu tertinggal di kantor fakultas, saya mau tidak mau kembali ke kampus siang ini.

Karena means because. It introduces the reason:

• Karena stempel itu tertinggal di kantor fakultas = Because the stamp was left behind at the faculty office

Indonesian often puts the reason clause first, just like English can:

• Because the stamp was left behind..., I have to go back...

You could also reverse the order:

• Saya mau tidak mau kembali ke kampus siang ini karena stempel itu tertinggal di kantor fakultas.

Both are natural.

In Indonesian, demonstratives like ini and itu usually come after the noun:

• stempel itu = that stamp / the stamp
• kampus ini = this campus
• buku itu = that book

So stempel itu is the normal word order.

Also, depending on context, itu can sound like:

• that stamp
• or simply the stamp if both speakers already know which stamp is meant

Here, tertinggal means left behind.

So:

• stempel itu tertinggal di kantor fakultas = the stamp was left behind at the faculty office

This is a very common Indonesian way to express that something was accidentally forgotten somewhere.

A useful nuance:

• tinggal by itself often means to live/stay or to remain
• tertinggal often means something like was unintentionally left behind

Examples:

• Tas saya tertinggal di mobil. = My bag was left in the car.
• Saya tertinggal dompet. is less standard than Dompet saya tertinggal or Saya meninggalkan dompet saya depending on meaning.

In this sentence, ter- gives a sense of an accidental or resulting state, not a deliberate action.

Because the meaning is different.

• tertinggal = got left behind / was accidentally left
• ditinggalkan = was left by someone and often sounds more deliberate

Compare:

• Stempel itu tertinggal di kantor.
  = The stamp got left behind at the office.
  This sounds accidental.

• Stempel itu ditinggalkan di kantor.
  = The stamp was left at the office.
  This can sound more intentional or more like focusing on an agent’s action.

In everyday Indonesian, tertinggal is the natural choice for forgotten items.

It means at the faculty office.

Breakdown:

• di = at/in
• kantor = office
• fakultas = faculty, department division in a university

So kantor fakultas is a noun phrase meaning something like:

• the faculty office
• the office of the faculty

Indonesian often puts nouns together like this without of:

• kantor fakultas = faculty office
• buku sejarah = history book
• ruang dosen = lecturers’ room

Yes, literally it looks like want, not want, but as an expression it means:

• whether I want to or not
• like it or not
• I have no choice but to

So:

• saya mau tidak mau kembali ke kampus
  = I have no choice but to go back to campus

This is a fixed expression and very common.

Other examples:

• Mau tidak mau, kita harus menunggu.
  = Like it or not, we have to wait.
• Dia mau tidak mau menerima kenyataan itu.
  = He had no choice but to accept that reality.

Indonesian does not always translate ideas word-for-word from English.

English says:

• I have to go back

Indonesian here says:

• Saya mau tidak mau kembali ke kampus

This does not literally contain a verb meaning must or have to, but the idiom itself expresses forced necessity.

Other ways to express obligation would be:

• harus = must
• perlu = need to

For example:

• Saya harus kembali ke kampus siang ini. = I must go back to campus this afternoon.

But mau tidak mau adds the idea of reluctance or lack of choice, which harus alone does not always emphasize.

Yes, they are related but not identical.

• kembali = return / go back
• balik = go back / return in a more casual, everyday style
• pulang = go home

In this sentence:

• kembali ke kampus = return to campus

You could also say:

• balik ke kampus in casual speech

But pulang ke kampus would be wrong, because pulang specifically means returning home, not just returning to any place.

So:

• Saya kembali ke kampus. = I’m returning to campus.
• Saya pulang ke rumah. = I’m going home.

Because ke marks movement toward a destination.

• ke kampus = to campus
• di kampus = at/on campus

Since the speaker is going back somewhere, Indonesian uses ke:

• kembali ke kampus = return to campus

Compare:

• Saya di kampus. = I am on campus.
• Saya pergi ke kampus. = I am going to campus.

Siang ini means this afternoon or sometimes later today around midday/daytime, depending on context.

Breakdown:

• siang = the daytime period around noon to afternoon
• ini = this

Common time expressions:

• pagi ini = this morning
• siang ini = this afternoon / this midday
• sore ini = this late afternoon
• malam ini = tonight / this evening

In natural English, siang ini is often translated as this afternoon.

Indonesian usually does not mark tense the way English does.

The sentence does not change the verb form for past, present, or future. Instead, time is understood from:

• context
• time expressions
• logic

Here:

• siang ini tells us the return will happen this afternoon
• tertinggal tells us the stamp is already in a state of being left behind

So even without verb tense endings, the meaning is clear:

• the stamp was left behind earlier
• as a result, the speaker has to return this afternoon

If needed, Indonesian can add time words such as:

• sudah = already
• akan = will
• tadi = earlier
• kemarin = yesterday

The comma separates the reason clause from the main clause:

• Karena stempel itu tertinggal di kantor fakultas,
  reason
• saya mau tidak mau kembali ke kampus siang ini.
  main statement

This is similar to English when a because clause comes first.

In informal writing, people may sometimes omit punctuation, but the comma is standard and helpful here.

It is mostly neutral to somewhat formal.

Why?

• kembali sounds a bit more formal than balik
• kantor fakultas is standard institutional vocabulary
• mau tidak mau is a normal idiomatic expression and works in both speech and writing

A more casual version might be:

• Karena stempel itu ketinggalan di kantor fakultas, saya mau nggak mau balik ke kampus siang ini.

Differences:

• ketinggalan is very common in speech for left behind
• nggak is informal not
• balik is more casual than kembali

So the original sentence is perfectly natural, especially in standard spoken or written Indonesian.

Yes, stempel is a normal Indonesian word. It is commonly used to mean:

• stamp
• seal
• sometimes a rubber stamp used in offices

In administrative or office contexts, stempel is very common and natural.

Depending on context, Indonesian also has:

• cap = stamp/seal, often more traditional or also used in formal/legal contexts

But in everyday office language, stempel is extremely common, so the sentence sounds natural as it is.