You set your timeout to 0, which means that there are Zero Seconds for Grub menu to appear. The Zorin OS Default is 10. I do not recommend less than 5.
You can set the timeout to 5 or 10, then tap ctl+o to overwrite. Tap enter to save current configuration. Tap ctrl+x to exit the editor.
Now you must run
sudo update-grub
for the change to take effect.
Then reboot, and tap the esc key as before and see if you can access Grub Menu.
You really want to be able to access it in case you need the Recovery Menu someday.