honestly, everyone has one leg shorter than the other, usually as much a quarter inch...

and a little fyi, a wedge and a shim are two completely different things, used for two completely different reasons. if you have one leg shorter than the other, you can try using a shim the length of the difference on the shorter leg to even it out. your knee not tracking straight is a completely different issue though, which usually has nothing to do with one leg being shorter than the other, it just has to do with your pedal stroke. a wedge may help that, and it may not, but i would see a professional about it before you start trying to fix the problem yourself and maybe worsen the problem...