Sketchup troubleshooting- need help!

I’m trying to open my file that I saved about 12 hours ago and I get an error message that says “unexpected file format.” How is this possible? and how do I fix it? I have to turn this thing in in less than 8 hours and I have quite a bit of work to do. Anything is appreciated!

Where have you been saving the file? Did you check the .skb file to see if it will open?