this plane has a 2 servos elevetor set-up, double check if both servos are arrange to give you same throw, like position of the servo arm, amount of movement, horn position, etc..

Now regarding just one aileron working, yes a plane may behave that way; check both, ailerons and elevator servos working as a team, test flight it again and let us know your results.

The right prop for your plane/engine is an APC 12.25x3.75, a 10x6 is ok but will not get all the juice out of your combo.