I Did Something Really Stupid

I need help. Desperately. I was trying to change my short name for my computer. Okay...stupid idea already, I know. So I changed the name of my home folder (from Betsy to Kate). So the only thing that happened was the name change. So then I change my mind and try to change it back to Betsy...then it says that the name Betsy is already used. I have no idea what that means. So I foolishly restart my computer and now everything is screwed up. I still have all of my old files under Machintosh HD > Users > Kate

I'm freaking out right now, did I make a new user? How can I make everything the way it was? And just how badly did I screw up?

Thank you for any help at all. I'm super scared that I'm going to lose everything!