Hello Brian,
I have tested with a bit of an older Chromebook and the CTRL+Shift+F works for me, you may very well need to perform a factory reset on your Chromebook to get it working correctly again. As everything is saved in the cloud a Factory reset should not cause any problems, but to be safe you should definitely backup any files saved on the Chromebook first with a USB drive.
To factory reset an Acer Chromebook, you can try these steps:
Sign out of your Chromebook
Press and hold Ctrl + Alt + Shift + r
Select Restart
In the box that appears, select Powerwash
Select Continue
Follow the steps that appear and sign in with your Google Accoun