Just don't go overboard with pressure or you'll end up breaking some of the wood inside. I think the warp thing must be pretty common. I just finished a 2nd US40 and noticed the warp after everything was together - Ahhhhhhhhh!

Then I went back and look at the destroyed UltraStick (thus the 2nd one built) and saw that the stab there also had a warp. However the plane flew that way like it was on rails. The destruction of the plane by the way had nothing to do with the warp in the stab, someone happened to turn on who shouldn't have.

In any case you probably won't get all the warp out so don't get to frustrated. It will probably fly just fine.

PS Make sure you laterally balance the plane, especially if you have a side mounted engine, otherwise it tend to fall out of a loop unless you correct it during the manuver. Great plane.