I am quite upset. I wiped the area immediately below the gas tank door with one of those gas-station wipes and it looks like I scratched the paint finish. Any ideas on how to deal with this?

I have had good luck with products from Griots Garage. I'd try the Fine Hand Polish first as the abrasives break down quickly and are less likely to damage the "good" paint around the scratch.
You can order at www.griotsgarage.com.

If that doesn't do it, try Gs27 available at Pep Boys., Walmart etc.