Oh dear. Not nice.
If Windows, open the Task Manager (Ctrl Alt Del and choose Task Manager). Click on the Applications tab, select Photoshop and click on End Process. It might take a while to respond.
Thank you. But, I have a MAC!! Suggestions for that?
Sorry. I don't do Macs, but plenty here who do.
move cursor to APPLE logo at top left of menu bar. press and drag down to FORCE QUIT, and then let up. (click on apple logo, drag to force quit....)
A panel will appear, hightlight photoshop to force quit it.