[Punchit]

There are a lot of great polishes out there that should remove just about any scratch you have as long as it's not through the paint. If the scratch is somewhat deep but not through the paint then your going to need a heavier grade cutting polish. Poorboy's offers a range of polishes that should help you out. As for the gas cap it's hard to stop rust after it has started, I would replace the screws if you can and apply a good wax/sealant all around the area, maybe even multiple coats. Let me know how that works out for you.