Remove your control arms from the servo. Turn on the plane and transmitter and nutralize aileron trim. install the servo arms so the arm and the control rod make a 90 degree angle. readjust the clevise at the contol horn on the aileron so that the aileron is nutral. If you do not have a clevise on the aileron control horn and have a Z bend adjust where aplicable. if it is not adjustable replace the setup with adjustable control rods. Recheck for aileron differential.