+ 1 for everyone who said it's not a big deal. But, if you really want to fix it, and if money and availability are issues, it's probably easier to replace the cog with a 3/32 one. There are plenty out there in a variety of sizes, and none should run more than about $20. Add $12 for a run-of-the-mill road chain, and you are ready to rock. I've been running a 3/32 drivetrain on my bike for years without incident, and it makes it easier for me to cannibalize chainrings from abandoned ten-speeds.