If the covering is loose it most likely causes your problem. Tighten it evenly and iron it one more time to the wing ribs.

Sealing on control surfaces makes controls more precise and therefore that is recommended for aerobatic models. If the distance between aileron and wing is same on both sides it is not necessary for you to seal the cap. And it propably does not cause your problem.

Sometimes it can be done ironing strips of covering to the V-croove at the pivot line. But the aileron should still move easily afterwards.