How do I tell if a new full view gl storm door is warped?

I have installed several full view gl storm doors without any problems, but the one I'm installing right now is not fitting properly. The lower portion of the door (on the side that opens) fits snug, but the top portion (on the side that opens) is out about 3/4 of an inch. I haven't put the closer on yet, but I know that it won't bring it in 3/4 of an inch. I tried putting shims toward the the bottom of the door (on the hinge side), and that brought the top in a little. I also tried shimmimg the side of the door on the opening side (toward the top), but it didn't do much to help. I have eyeballed the door, and used a string to try to see if it is warped, and with these non-professional methods, it doesn't appear to be. Any suggestions?