You are able to keep your Whiteboard in full screen even after refreshing the page.
First click on the Full-screen Whiteboard mode button: 
NOTE: The whiteboard in the Full-screen Whiteboard mode is slightly different to the regular view, please find more details HERE.
Then toggle the persistent browser's full-screen mode to ON and OFF:
Windows: Press F11
Mac: Press Command ⌘+Ctrl+F or Command ⌘+Shift+F
NOTE: The key combination may differ depending on the local settings of your PC and browser.
ALSO NOTE: Microsoft Edge browser does not support this feature.
Chromecast users should select the cast tab and then click on Full-screen Whiteboard mode button, not the browser's full screen option.
We hope you found this information useful!