I saw your video, something is binding! I would first swap the control horns sot they are on the same side of the aileron, so your linkage will move both ailerons the same distance. As I said before some one at my club was having the same issue, and the linkage was the cause.
Or it could be a weak servo and you can just disconnect the linkage to the ailerons from the servo and see it you have the same force and amount of movement generated by the servo in both directions of travel.
Another thing to check is that the servo horn is symmetrical and not an offset type used for aileron differential.