YOU SAID:

I was just gonna go to that concert over there

INTO JAPANESE

あそこのあのコンサートに行くつもりだった

BACK INTO ENGLISH

I was going to that concert there

INTO JAPANESE

あのコンサートに行っていた

BACK INTO ENGLISH

I went to that concert

INTO JAPANESE

私はそのコンサートに行きました

BACK INTO ENGLISH

I went to that concert