Just a quick suggestion, if you are using torque rods- if you use the e-z links on the ends of the servo arm, with the radio on and centered, you should have no problem centering the ailerons. However with that said I have also found with this type of linkage, it's possible to have unequal throws. Not alot, maybe even not enough to notice.

If you are trying to use z bends on the rod and the servo they could very well be unequal lentghs.

I am with Overboard on this- post us a pic to get a good look at it.