If I accidentally close the SKP file and when re-open it , it said it is not a sketch up file. but it contains 7 MB.
Hang file Lawrence Japanese bath tub for sketchup.skp (7.1 MB)
It’s nearly 30% zeros and the first part is missing.
This is the first part of your file in a hex editor.
The first part of a viable SketchUp model looks like this in a hex editor. On the right you can see it says it’s a SketchUp model.
Where wwas your file saved while you were working on it? Are you using a cr acked version of SketchUp? Do you have a .skb backup copy of the file?