YOU SAID:

If my pants were too tight, then my pants wouldn't fit me.

INTO JAPANESE

ズボンがきつすぎると、ズボンが合わなくなります。

BACK INTO ENGLISH

If the pants are too tight, they will not fit.

INTO JAPANESE

パンツがきつすぎると、フィットしません。

BACK INTO ENGLISH

If the pants are too tight, they will not fit.