Is there anyplace to retrieve if you forgot to save?
where do I find the user folder?
The answer depends upon what you actually did.
No; if you never saved the file at least once before you closed SketchUp.
Yes; if you saved the file at least once before you closed SketchUp.
Yes; if SketchUp crashed >5 minutes after you began a new unsaved modeling session.
An Auto-Save file is a temporary file available on the file system while SketchUp is running.
The only occasion an Auto-Save file is saved to disc is when SU closes abnormally (crashes).
In your situation, SketchUp didn’t crash, you say you simply closed it without saving.
Thus, the Auto-Save file was automatically deleted upon closing the application.
Auto-Save — SketchUp help
Upon the first Save command in a new modeling session SketchUp writes just one *.skp file to disc.
Only upon subsequent saves of that existing *.skp file does SketchUp begin to write a Backup *.skb file.
Thus, if you closed SU and did not Save at least once there is no *.skp or *skb file saved.
Backup — SketchUp Help