How to access a FCP backup

I was editing today and suddenly got an error my drive was full. The entire project disappeared off FCP screen. I thought my file was on my larger drive but somehow I missed the default location. I manually moved the FCP project file from my computer to the external drive but it will not open. When I try and access the back up The "access backup menu choice" won't highlight when I open FCP. How do I access my backups? What is the proper way to move a FCP file from one drive to another when FCP closes everything because of no space? Seems you would build a little redundancy into FCP so it could give me a little warning? Seems crazy I would get the error when it's too late to recover my work. Thanks for any help recovering a ton of work.