Are they both the same? Most gliders have washout which the out board trailing edge is up just a bit. Makes the center stall first.

If it is just one wing, you can try fixing it with heat. I would heat the obichi a little bit, and twist while you are doing it, then hold it in place as it cools. You can also do it with the covering after you cover it, but that would take a bit more being fully sheeted. It won't want to twist. Hope that works for you.