If everything looks straight but it rolls try adding a washer to the engine mount on the left side, so that the engine thrust line angles to the right a little. I had the same problem although not as bad, and this really helped.

You are using the same battery as me, which is bigger than the designer really intended, so you (like me) probably fly it faster than intended. The wing will indeed twist at speed. And if you fly in heavy (5+ mph) wind like me, you might also see the tail flutter.

I reinforced both the main wings and the tail with cf rod.
Clark