Wellllllllllllllllllll

About your horns......

A couple of suggestions:
It is always worthwhile to have the servo arm connection closer to the servo and the connection on the horn on the surface farther from the hingeline. The idea is to give the servo the mechanical advantage. It's also worthwhile to give the surface less mechanical advantage. The way you have your connections, the servo has the least advantage to move a horn that is going to have even more advantage resisting that servo.

I would suggest that the leverages that're present will contribute to the problem you're having. They will also help the aileron flutter beat the servo's gears to death.