Oops, I did it again!

I have 3 electrical cabinets that I have emptied of all the useful
bits and would like to make them into lock-up cupboards. They are 2
mm. mild sheet and stand about 6 ft. high and 3 ft wide with a depth
of about 9 inches.

The doors are having a folded and welded edge for strength, but
because there were a lot of switches and lights etc. there before they
left a lot of holes which needed to be filled. I made some disks of
the correct sizes and thickness and MIG welded them in the holes. This
was in the first door. Smashing, all I needed was to grind down the
welds smooth, a bit of filler and paint. Oh no! The panel has now got
two stable states, both wrong. The panel is distorted and I am
dismayed. Is there any way I can relieve this and make it flat again?

Does anyone have a solution? I would be very happy to try anything.

Thanks and regards George.