I pressed the little pin at the top right of the properties panel and it pinned the current property that I was in (particles) and now all of the other options are gone. I’ve tried loading the file without the UI Layout option selected and it still doesn’t revert it to the default layout.
Also, the T and N menus don’t fill to the bottom of the screen as before. How do I change this? (Although I kind of like this view.)
Looks like a 2.79 file that you opened in 2.80. You might try restarting 2.80, then go to open the .blend file, and at the open dialog/file browser uncheck the [ ]Load UI box in the lower-left and that should get you the file but retaining the default 2.80 UI.
If it’s something persistent that you see each time you start 2.80, you can always delete the config files or invoke Blender from the command line with the --factory-startup option or do File->Load Factory Settings and see if that fixes it.
Also, if you click the Particles tab in the properties, you should see the pin icon (only the tool properties doesn’t show it) and that should let you clear it and might get you your other property tabs back.