That’s my thoughts too. I at first thought there was about a quarter-inch twist. But further investigation showed there was a built in washout which was the majority of what I saw. The actual twist, once I was able to get the a level board, is abut 1.5 mm at most from left to right and front to rear even less. so it is a minor issue. It's my own fault though, I thought the thin board I had, that was reinforced by 2x4 would be flat enough and level. but alas, I was just a dumba#$. I now have a nice THICK board that and should no longer have the issue. My only saving grace is that I was attentive enough to notice it before finishing the wing and then having to try and fix or trim it out possibly causing the plane to be unstable.