Problem setting Grub password on RHEL7

I'm sure I'm missing something very simple, but can someone help me with this?

Trying to set up a password so that the Grub menu can't be edited without authentication.

1. grub2-mkpasswd-pbkdf2
   Enter password:
   Confirm password:
2. Copy password hash
3. Edit /etc/grub2/40_custom
   set superuser="root"
   password root
4. Save file
5. grub2-mkconfig -o /boot/grub2/grub.cfg

After rebooting, I enter 'e' at the boot menu. It prompts me for the user (I enter 'root') and then it prompts me for the password (I enter ) and then I'm back at the Grub menu.

What am I missing? This seems like it's supposed to be much easier than all this.