[Kevin in NJ]

It is good that you know the metal must have the correct shape before you try to weld it in place.

It is a compound curve.

You need guess where to stretch the metal with some hammer on dolly work.

They may not have taught you this, but you must understand the each weld is a shrink point. You must level the metal at the weld (I am assuming you are MIG welding) and do some hammer on dolly work to level the metal.

Keep in mind you need to do some small welds across the face, jumping around. Then grind and hammer. Keep that up till you have it fit.

With a bit of practice it is not hard to get a panel that just needs a few coats of a filling primer to be level.