اشتريت بالضبط خمسة ليترات بنزين.

A simple Levantine-style pronunciation would be:

ishtarēt bizzabt khamse lītrāt banzīn

A few notes:

• اشتريت → ishtarēt = I bought
• بالضبط is often said more like bizzabt in everyday speech
• ليترات = lītrāt
• بنزين = banzīn

If you want a more natural casual Levantine sound, many speakers would say something very close to:

ishtarēt bizzabt khames lītrāt banzīn

It is understandable in Levantine, but it sounds a bit neutral / semi-formal / close to Standard Arabic.

A more everyday Levantine version might be:

• اشتريت بالزبط خمس ليترات بنزين
• اشتريت خمس ليترات بنزين بالزبط

Why?

• بالضبط is often written/spoken in dialect as بالزبط
• خمسة often becomes the shorter colloquial form خمس before a noun

So the original sentence is fine, but it is not the most strongly colloquial version.

Because the verb itself already includes the subject.

• اشترى = he bought
• اشتريت = I bought

The ending -ت tells you the subject is I.

So:

• اشتريت = I bought
• أنا اشتريت = I bought with extra emphasis on I

Arabic often leaves out subject pronouns when the verb already makes the subject clear.

بالضبط means exactly / precisely.

In this sentence, it emphasizes the quantity:

• اشتريت بالضبط خمسة ليترات بنزين
  = I bought exactly five liters of gasoline.

You can move it around a bit:

• اشتريت بالضبط خمسة ليترات بنزين
• اشتريت خمسة ليترات بنزين بالضبط

Both work. The version with بالضبط before the number puts the focus more directly on the number itself. The version at the end often sounds a bit more conversational.

This is because Arabic numbers have a gender agreement pattern that is often surprising to English speakers.

With numbers 3–10, the number usually shows the opposite gender of the noun being counted.

Here, ليتر is generally treated as masculine, so the number appears as خمسة.

So:

• ليتر → masculine
• therefore five liters → خمسة ليترات

In everyday Levantine, though, you will very often hear the shorter form:

• خمس ليترات

So:

• خمسة ليترات = more careful / more standard-like
• خمس ليترات = very natural colloquial Levantine

The singular is:

• ليتر = liter

The plural here is:

• ليترات = liters

In more standard grammar, after numbers from 3 to 10, the counted noun is usually plural, so:

• خمسة ليترات = five liters

Since ليتر is a borrowed word, the sound plural -ات is very common:

• ليتر
• ليترات

That is a normal and expected way to pluralize this kind of word.

Because Arabic often expresses measurement phrases without a separate word for of.

So:

• خمسة ليترات بنزين
  literally looks like five liters gasoline
• but it means five liters of gasoline

This is very normal in Arabic.

You can also say:

• خمسة ليترات من البنزين

That is grammatical too, but the version without من is very common and natural in measurement expressions.

Yes. بنزين is the normal everyday word for gasoline / petrol in Levantine.

So if you are talking about fuel for a car, بنزين is the usual word.

A learner should know:

• بنزين = gasoline / petrol
• بترول usually means petroleum / oil, not the everyday word you would normally use for what you buy at the pump

So in this sentence, بنزين is the right everyday choice.

Not in Levantine.

In normal spoken Levantine, you do not pronounce Standard Arabic case endings. So you would just say the words as they come:

• ishtarēt
• bizzabt
• khamse / khames
• lītrāt
• banzīn

That is one reason this sentence feels easier in dialect than in fully formal Standard Arabic.

A very natural colloquial version would be:

اشتريت بالزبط خمس ليترات بنزين

or:

اشتريت خمس ليترات بنزين بالزبط

If you want it in easy transliteration:

• ishtarēt bizzabt khames lītrāt banzīn
• ishtarēt khames lītrāt banzīn bizzabt

So the original sentence is correct and clear, but if your goal is everyday spoken Levantine, these versions sound more native-like.