[dsraven]

did you mig weld the panel? mig welding doesn't love to be hammer on dolly too much after it cools off, it tends to get hard and crack if too much work is done. there are softer wire alloys that can work a bit better than others
if cutting a hole on the inside you could tack some flaps onto the door and then screw the cut out piece to that. not much heat generated that way. if you wanna weld it back in then do small welds, one here one there but not close together so the welding heat will be more spread out. let the panel cool to room temp between welds if they start getting close together. like wait till you could put your tongue on it. I find having another job to do between welds is a good idea. wait now, or spend that time later doing body work.
weld, hammer on dolly when still hot, like red, that stretches the metal. it cools and shrinks back to a more normal size.