YOU SAID:

Fill up my car while you're at it.

INTO JAPANESE

あなたがそれにいる間に私の車をいっぱいにしてください。

BACK INTO ENGLISH

Fill my car while you are in it.

INTO JAPANESE

あなたがそれにいる間に私の車を埋めてください。

BACK INTO ENGLISH

Fill my car while you are in it.