My 64 C-10 fleetside shortbed build

[allaboutchevelles]

I borrowed my cousins stud gun and started trying to attack the dent in my roof. Can any good body guys give me some advise on getting this dent right??? I got the small crease pulled out and the dent is gone now BUT the metal is flimsy now. it pops in and out, if it would stay pulled out then it would almost be perfect but with a slight push it pops back in. the area is about a 6 inch diameter. if you look at the pic you can barely see the purple marker where I outlined the spot. I pulled a small string from one side of the cab to the other side so I could see the low spots. if I pull the dent out its about perfect but when u push it goes back in, How can I fix this???