Campgems' response is good. Google 'stretching metal'. Get a plastic mallet and a nice hard flat area to do the whacking (anvil, 1/4 sheet steel plate, etc) and 'whack' gently the peice of metal in the center and toward but not to the edge in question. You will stretch the metal in the center causing it to bulge ever so slightly. If this is too much work then add Elmer's wood putty to that low spot and level it 'by judicious application of sandpaper'.[sm=idea.gif]