Corrupt Garageband file? HELP!

Hi. I've worked 20 hours (over multiple sessions, multiple weeks) on a song in garageband. Today, while working on it some more, I could tell I was running low on memory. I should have backed up the file.

Then Garageband hung up while I was trying to duplicate a track. So I did a force quit after a long time of waiting.

Then I shut down, restarted, and opened Garageband. Now I get this error message:

READ ERROR!
Illegal format of file

I'm afraid my file is corrupt. Can someone tell me if this is fixable? If not, can I somehow pull up yesterday's version?

Thanks,
Steve