I had the same problem with my bootlegger, it was very bad. What I did was line up one side and completely seemed it up. No problem doing that. But it made the other side worse.
With some sticks on the inside and taping the outside I was able to bring the curled part out and the good side a little in. I did the inside first then the outside.

I would not have been able to do it this way without very strong tape. The tape I used was 2" shrink wrapping tape. This tape is great. You can pull and pull and it will stretch a little hold great.

I am no pro at building and I don't want to give out bad info so please take note of that.

Marc Donnelly