Hi
To start with make sure everything on the TX is centred and trims at zero. Then check the arm on the aileron is centred properly so that the holes are in line with the hinge line. Check that the accuator rod is as straight as it can be eg. 90 degrees from the trailing edge.

When installing the servo arm on the motor the arm should point toward the leading edge a little and the other wing should match. In other words if you turn the wing upside down abd have the servo looking at you the arm should be about 10 o'clock. This will give you differential aileron - more up movement than down. This movement should be matched on the other wing if you have matched the servo arms up the same. The effect of this is, for example , turning right using ailerons, the right aileron goes up more acting as a bit of a wind brake dropping the wing and the lift on the left wing created by the lowering of the left aileron is enhanced a little.

I hope this makes sense!!!!!!

Let me know if does or you need a drawing if- I can work out how to post one

Cymaz