To twist the wing properly you just about need 3 hands! I place the wing between my legs to stabilize it, twist in the washout with one hand, and use the heat gun with the other. Do both sides, each with between 1/4 to 3/8ths inch washout, and be sure to get it as equal as possible between both sides.

Over the years, every time I walk besides any full-sized aircraft, I usually sight down the trailing edge. You would be surprised just how many man-carrying aircraft use this technique.

Yes, it usually takes a lot of force to twist the wing. This is good however, as it indicates a strong structure. My landings were stable, and just about as slow as anyone could want. Best of luck.