You need to put an incidence meter on each panel. Check to ensure that from root to tip they are both the same. If they are than bolt them to the fuselage and check again. You have either a bad wing panel or the alignment pin. It may also be were the alignment pin enter the fuselage. Misaligned wing panels act like ailerons. If your lucky it will be the alignment pin and that is an easy fix. I have been there with ARFs. Another thing to look at is the horizontal stabilizer for proper alignment in relationship to the trailing edge of the wing panels.