My garageband tracks got randomly messed up and changed, and I did not do anything?? Do not know how to get it back to original?

I recently recorded a piano track on garageband by connecting my electric piano to my Macbook air through a midi/usb cord, and my audio interface connected. I was playing and hearing through my headphones, and garageband was receiving the sound and exact keys being played (like a midi board). I had the track completely recorded and SAVED, and I even recorded a second track of vocals with it, and saved the entire project. A few days later, I went back to open it, and found that my piano track had changed? It sounds as if someone went in and modified it, as if they changed what was recorded. It seems like everything is just one chord on each first beat of each measure, and it is a lot of chords I absolutely did not record. I am positive I did not record over it, nor did I do anything to change it, I simply saved the project. I cannot figure out what has happened to it or how to revert it back to normal, and cannot seem to find any related questions anywhere on the internet. I am really upset!!