Im teaching myself how to hammer and dolly to get the dents and welding warp out of the rear quarters on my 52 chevy 4 door. The problem is I have a spot about the size of a basketball that keeps poping in and out. I know this means the metal has stretched, but how do I get it to shrink back? I am having a hard time because the inner fender is limiting my access to the back of the pannel. I outlined the section. It is a very small distance fron in and out. How do I fix this?