Sounds like a little wing warp or surface warp. All my plane's have a small amount of this too. H-9 P-51 60 scale is one of them. I think it has to do with many thing's. Wing warp, flap / aileron warp, the position and centering placement of the hinge' (s), heat or cold stretching the coating and causeing warp. I set the outside or wing tip surface's as flush as possible and work toward the fuse. Works for me. I have a GP Stuka with the detached dropped aileron and flaps. They are real fun to get rite.
Good Luck, I'm sure it will work out with a little extra trim.
Just my 2 cents
JWA