I'm afraid you'll have to restore from back up and re-enter anything since then.
If you find, in future, that a file is growing significantly larger (even though you may have entered only a few changes)
1. Save the file as a Project database (.mpd)
2. Exit Project
3. Start Project
4. Open the .mpd file
5. Save the file as a Project file (.mpp)
6. Exit Project
I hate to be the bearer of bad news, but that is the only program I have found and can suggest.
Have a good night and god bless!