RE: What is wrong with my cub
hi
a cub can be a real bitc.... to get airborne. the most likely problem is a warp in one wing panel as has been noted. also check incidence of horizontal stab and wing. wing should be no more than 1 to 1.5 degrees positive. if you are using struts be sure struts are of proper length so as not to distort wing incidence when installed. a cub is not a good first airplane to start to learn to fly with. you mentioned left thrust in engine...should have right thrust 2 to3 degrees right. and as stated check rudder to be sure you do not have right deflection in it.
good luck and happy flying
pt19 flyer