Wow the colors on him are beautiful!

He's so small too, what a cute little guy. I've heard of several really good breeders on the internet who know how to ship their turtles really so that they go through as little stress as possible. Actually, the smaller ones ship easier as their light weight is less likely to be shifted around during transit.
Congratulations on your new baby! He's a real champ!
I also agree with ice, you should go ahead and raise the water level so he'll have more room to swim around, but if he's happy right now, you should probably wait a few days for him to settle in. At this point I'd be worried about accidentally changing the water temperature too suddenly or drastically. He really needs to have some peace and quiet for a few days. If you do feel like adding water now just make sure to do it gradually and try to use the same temperature water as what's in the tank already.