If it's only 1/8 " twist it should be possible to take that out after covering, using the heat gun and twisting the other way as you play it over the surface. Hold it twisted until the covering goes colder, and it should straighten it.

Also, if it really is only 1/8" over the whole of one wing half, I would have thought the aileron trim will trim it out on the first flight.

Good luck!

-David C.