Carowinds offers about 14 credits depending on how you count Thunder Road and if you can get the small kiddie coaster (must have a child to ride).
It's a nice park overall, Intimidator and Afterburn are outstanding, and the rest of the coasters are pretty standard fare.
I'd also recommend taking the light rail downtown, there's plenty of good restaurants, (I recommend Mert'swhich is good soul food), museums, places to see and overall Charlotte has a very walkable and clean downtown. Visit http://www.ridetransit.org light rail info, but you could catch it at I-485 and South Blvd, and ride it all the way in to downtown. It's a good way to see part of the city, and enjoy downtown. Plus South End has a lot of cool places too.