Sounds like you changed the name of the administrator ACCOUNT, not the password.
To be blunt, this will be a right mess to fix if I'm correct about what has happened. The only good news I can give you is that your data is still on the machine somewhere, but putting things back the way you had them will be a nightmare. I'd highly recommend seeking out a Mac tech *with experience with this problem* to have them restore things.
If you used Time Machine regularly, you could also just erase the drive and start over from a TM backup before you changed the admin name, which would be a lot easier (but would lose any new files created since the disaster of course).