I meant to add, make yourself a belt alignment tool from the correct length - whatever's right for your car - 1/4" x 1" aluminum strap.

I have several different lengths of 1/4" x 1" aluminum for straight edge use.
Cheap and works well.

You should be able to get 4 points of the pulleys flush against the belt.
IE: upper and lower point of the alternator pulley, upper and lower point of the crank pulley etc.
They should all touch indicating the pulleys are spaced out correctly as well as being in line.