twostroke:

It's not uncommon to have a panel warp after covering.

What you have to do is hold the panel with the opposite twist, and reheat the covering.

Do it a little at a time, do the top once, then the bottom the next time. Switch back and forth, top to bottom, until you have it straight.

Sounds like a bother, and it is, but not much of one.

And as you continue to build, you'll get to where starightening a panel is just another part of film covering.

HTH

Bill.