YOU SAID:

this is the worst party I've ever been to

INTO JAPANESE

これは私が今までに行ったことが最悪のパーティーです

BACK INTO ENGLISH

This is the worst party I have ever done

INTO JAPANESE

これは私が今までやったことがない最悪のパーティーです

BACK INTO ENGLISH

This is the worst party I have never done before

INTO JAPANESE

これは私が今までやったことがない最悪のパーティーです

BACK INTO ENGLISH

This is the worst party I have never done before