Your rudder linkages may be set up too sensitive... Try moving the clevice to a hole further from the hinge, or moving the connection at the servo closer to the output arm retaining screw.

Trainers have "roll-yaw coupling." When you give rudder input, they will roll in the direction of the rudder input, almost as if you used the ailerons. (sometimes quicker than the ailerons...) This is primarlly due to the dihedral of the wing.

The only way to get used to using the rudder is to fly and purposefully make turns avoiding use of the ailerons.

Its a good thing to practice, as you may find that the aileron servo accidentally comes unplugged in flight smoe day. Knowing how to fly using the rudder can save the plane. I've seen a plane landed safely with both ailerons just flapping freely (both clevices popped free... Note: reduce power to make the ailerons quit fluttering if this happens.) I've landed a plane after a mid-air collision which ripped an aileron loose (clipped 6 inches off the wing too...) and disabled the other aileron.