Fixing Warpage.....HELP!

I shaved my doors and the first one was fine, but the second one I did warped a very small amount. It's about the diameter of a golf ball and it sucked in just below where the handle used to be. I can push it back out from the inside of the door, but it just pops right back in. What can I do to push it out and make it stay? I don't want to bondo over the warp to cover it up. And I don't want to go to a body shop...I'd like to learn how to do it myself.

Thanks,Chris