1997 chevy cavalier new gator belt will not go on properly. The tensioner always takes distance away instead of creating the proper gap required to install belt. Please help

Either one of two things here, either the wrong belt, or the wrong routing of the belt.

You have to hold the tensioner back with a wrench in order to install the belt. The tensioner making the ID larger is the only way to have tension on the belt.

The belt routing is critical.

6815

I hope this helps.