Can't open, update or uninstall Photoshop -- getting 301 error

I can't open Photoshop on my Mac. It says the scratch disk is full. I tried pressing Option and Command when opening Photoshop. I got the Preferences box, but I cannot make *any* changes in that box. I tried to uninstall Photoshop both from Creative Cloud and from my hard drive. In both cases, I got a "failed" message. I can't open the app. I can't update. I can't uninstall. I need this app. What do I do?