YOU SAID:

I went to a party once

INTO JAPANESE

私は一度パーティーに行った

BACK INTO ENGLISH

I once went to a party

INTO JAPANESE

パーティーに行った

BACK INTO ENGLISH

Went to a party

INTO JAPANESE

パーティーに行きました

BACK INTO ENGLISH

I went to a party

INTO JAPANESE

私はパーティーに行きました

BACK INTO ENGLISH

I went to a party