This is just a tip to prevent these warps in the first place.

When you put covering on the wing, don't shrink it until the entire wing is covered. Just iron the covering around the perimeter. Don't iron it to any ribs or shrink it.

Now take your heat gun and shrink it one rib bay at a time doing the top then the bottom. Work your way across the wing like this and most of these warps won't happen. I can't say it entirely prevents them but any warps the covering does induce are much more easily removed.

When you are done shrinking the covering, go back and iron it down to the ribs.