How do you know that you wing is "out of square"? When you start mounting your wing you need to pick point on the very rear center of the fuselage and then measure from that point to each wingtip. The distance should be the same for both sides. If those distances aren't even, then you plane will not fly correctly. Same goes for the stab. 1/4" is a lot in a model. But once again, how are you judging that it's not level?