It's a zen thing. A coordinated level banking turn requires aileron and small amounts of elevator and rudder added in. It is difficult starting out to throw differing amounts of stick deflection when you are trying to think about all three at once. Eventually you'll get so you can throw 20º of aileron along with 5º of opposite rudder and 10º or elevator, but initially your brain will want to do them all in equal amounts. Practice, practice, practice. Work out one control at a time and then work on blending them together.

Also, try switching perspectives (chase plane, zoom, etc.) to observe how the model is reacting to your throws.

In pylon you can "cheat" and bank the plane on it's ear and then turn by giving up elevator. If you apply a little elevator in with the roll it lifts the nose to hold altitude.

I can remember my first real instructor having me do big, expansive flat figure eights for whole tanks of fuel, over and over. Gets you practiced up in keeping level in the turns.