If ever making a gasket like that for a metal surface, the easiest and most accurate way to do it is by simply cutting out a piece large enough to overlap all edges then use a small ball peen hammer to go around all edges, essentially cutting the outline for you and then gently tearing off any excess that didn't simply fall off. Easy peasy.
I know Jon Bond Performance and others recommend a anaerobic gasket sealant for the mating surface.