I ended up having to create a new user name because the migration assistant wouldn't let me put the data back onto my original user name. I now have to log into the new user name to see all my data, apps, photographs etc. What went wrong?

I have a Mac that was part of the recall involved with the faulty Seagate hard drives. The folks at the Apple Store near me changed the hard drive early December, 2012. I had my data, etc. all backed up on a portable hard drive. When the Mac was returned with the new hard drive, I used the Migration Assistant to bring everything back over. Trouble was, it wouldn't let me bring it over to my original user name. I was forced to create a new user name that became the place where everything was restored. I can't see any data on my old user name, just the basics. Everything is on the new user name but I wish I didn't have it (just want everything back the way it was originally). Any suggestions?