GarageBand Help Needed

Here is my situation:

I recorded a live performance on a Boss Micro BR digital recorder. I converted the audio file to mp3 and imported it into itunes. It's ONE VERY LONG mp3 (45 minutes). I want to cut it into separate mp3's for each song of the performance using GarageBand, if possible. I have tried to drag the mp3 file into the track window in GarageBand. A box that says "Importing" pops up but then disappears and nothing happens. The file does not show up in GarageBand. What am I doing wrong?? I've searched the forums but can't come up with anything. I also should mention that I have very little experience with GarageBand.

Thanks,
O'D