Hi. I'm getting ready to install a new glass shower door in a fiberglass shower surround. The problem is the opening at the bottom and middle of the fibgerglass shower is 30" wide and at the top its 30 1/2" wide. Any advice on how to install the shower door given the fact that the top of she shower entrance is wider than the bottom? I know I can adjust the width of the shower door using the adjustable jambs but this still doesn't account for the problem. Thanks!

A picture would help butI am going to guess that the side walls are not plumb and proper reframing is the correct route to follow. 1/2" in the last 2' is noticeable and should be corrected.