I too just purchased and assembled a Super Cub as my very first RCplane. One thing Inoticed with my plane, which also may be the case with yours, is that the rudder and tail flaps needed a lot of adjusting before I flew it the first time. You have one clevis attached to the tail flaps, and that clevis can be adjusted by disconnecting it from the push rod and then turning the end of it clockwise or counter-clockwise until you see that the flaps are flat with the tail when your transmitter is powered on and the trim is set in the center. Do the same thing for your tail rudder as well.

My Super Cub also had a flaw, where the push rod on my tail rudder would pop loosein flight. My first flight was a scary one, because the plane would just go in circles until I could crash it down as softly as possible. Ifixed that issue by applying CA glue to the push rod fastener.