Hammer and Dolly lesson??

[prg machine]

I have a situation to share and maybe help others out as well as I figure this out, with the members help on this forum of course.

I am in the process of deleting the sidemarkers on a 68 front fender. Both right and left eventualy and the fleet bed as well. To start I chose the right front because it the usual rot at the front corner and also had about 2 quarts of bondo on it from an unexplainable series of dents and wrinkles that cover the whole thing. It looked good when I purchased but alas.......definetly in need of lotsa hammer and dolly etc. The fender is stripped and I have good access front and back. I figure the "bondo bucket repair" was done as a quick fix while the truck it came from was together. I have been guilty of similar " good enough for now " repairs in the past and can't pass blame on to anyone on this.
I ahave done a pretty good job of getting a lot of the dents straight so far and proceeded to delete the side marker. I cut a corresponding piece to fill with and was very careful to get a good fit to remain flush and not have gaps causing pulling and distortion when welded in. I tacked , hammered and cooled with air to not get too hot. As I proceeded the patch wanted to grow up and buckle . I carefuly peened out with hammer/dolly and caught a few more tacks....etc. etc. until all welded. The patch turned out good and fairly flat...........HOWEVER!!!! I now have a hand size concave area about a 1/2 inch deep at the deepest above that patch. It is spread smoothly out and is not straight forward to me how to proceed here. I tried a couple of heat shrink spots at the lowest area, heat a dime size spot red and then chill with compressed air. It seemed to be working.............BUT I stopped because I am now getting other distortion adjacent to the depression. Should I hammer dolly in a particular area?? On or off dolly?? I have no problem with the smaller stuff and even have removed very tight creases at the eyebrow area with only hammer and dolly.
Some wisdom is in order on this one as I feel like I might end up chasing ghosts and end up with another BOBDO Bucket repair. I realy wish to avoid this!!!!
Help????