syuuden ni girigiri maniaimasita.

終電（しゅうでん） means the last train of the day.

It usually refers to the final scheduled train you can take that night. So in this sentence, the speaker is talking about managing to catch that final train before service ended.

The particle に is used because 間に合う commonly takes に for the thing you make it in time for.

So:

• 終電に間に合う = to make it in time for the last train
• 会議に間に合う = to make it in time for the meeting
• 締め切りに間に合う = to meet the deadline / make it by the deadline

Using を here would be incorrect with 間に合う.

ぎりぎり means just barely, at the very last moment, or with almost no time to spare.

So it adds the feeling that the speaker did make it, but only by a tiny margin.

In this sentence, it gives the nuance:

• I just barely made it
• I made it at the last second

間に合いました is the polite past form of 間に合う.

• Dictionary form: 間に合う
• Polite non-past: 間に合います
• Polite past: 間に合いました

It means:

• was in time
• made it in time
• managed to make it

So 終電にぎりぎり間に合いました means something like:

• I just barely made the last train.
• I was just in time for the last train.

It is in the past tense because the speaker is talking about a completed situation.

They are looking back on what happened:

• the last train came,
• they got there in time,
• and now they are reporting that result.

In English, we also usually use past tense here:

• I made it in time
• I barely caught it

Not exactly.

終電にぎりぎり間に合いました focuses on being in time, especially barely in time.

It strongly suggests that the speaker successfully caught the train, but the emphasis is on the narrow timing, not simply the fact of riding it.

Compare:

• 終電にぎりぎり間に合いました。
  = I just barely made it for the last train.

• 終電に乗れました。
  = I was able to get on the last train.

The first one highlights the timing more.

Yes, 終電にぎりぎり間に合いました is natural.

Here, ぎりぎり is an adverb modifying 間に合いました, so it tells you how the speaker made it in time: barely.

You may also hear slightly different word orders, such as:

• ぎりぎり終電に間に合いました。
• 終電に間に合いました。ぎりぎりでした。

Japanese word order is fairly flexible with adverbs, but the given sentence is very normal.

No. That is not correct.

間に合う does not normally take を for the thing you are making it in time for. You use に:

• 終電に間に合いました ✓
• 会議に間に合いました ✓
• 締め切りに間に合いました ✓

So the pattern to remember is:

• [event / train / appointment / deadline] に 間に合う

Japanese normally does not use spaces between words in ordinary writing.

The standard way to write this sentence is:

終電にぎりぎり間に合いました。

Spaces are often added in learning materials to make the parts easier to see:

• 終電
• に
• ぎりぎり
• 間に合いました

So the spaced version is helpful for study, but not normal everyday Japanese writing.

The readings are:

• 終電 → しゅうでん
• に → に
• ぎりぎり → ぎりぎり
• 間に合いました → まにあいました

So the full sentence is read:

しゅうでん に ぎりぎり まにあいました。

Or without the learner spaces:

しゅうでんにぎりぎりまにあいました。