Failed to open project.Check it is a valid Construct 3 single-file

I saved the project and shut down the computer and the next day I get this error

The file may be corrupted. Try renaming .C3P extension to .ZIP and opening with Windows or WinZip.

The file may be corrupted. Try renaming .C3P extension to .ZIP and opening with Windows or WinZip.

I tried to open it as zip, it says the archive format is unknown or corrupt. the file is corrupted