The previous stresses on the area around the hole stretched the metal. The more you hit it, the worse it will get. First read the surface of the metal and estimate where it has stretched. Then you can shrink by applying heat to one small area at a time and then applying hammer and dolly while it cools. When you see the metal shrink and the flimsy oil can tighten up, you will be amazed. After you shrink a couple small areas, read the metal again. You can over shrink an area and create a new problem. Suggest you pick up a piece of 18 or 20 gauge sheet steel, create a stretch with a hammer, and practice with hammer and dolly. You can also shrink with heat and a wet rag or heat and compressed air. Bondo or glazing putty are not a substitute for the needed metal work. Especially on a flat-ish area like the gas tank hole area.