Holding down the shift key on booting does not work
Zorin forum sticky specifies the Left shift key.
Every distro I've used in the last 15 years have another feature you can use if you remember the root password.
Boot as you normally do. When you get to the login screen, press ctrl+alt+F1. That will take you to a text-only terminal. Login as root, and reset your user password from there.
Then press ctrl+alt+F7 to get back to your login screen to use your new password.
There is also a somewhat more complicated method booting a livecd, mounting your Zorin partition, and editing /etc/password and /etc/shadow to remove the user password (must be done is a specific way). Then you can login without a password and reset your password. I leave it to you to do the research to find the instructions.