@justjim1220 OK, I’ve been banging my head on this, and it turned out to be two different things:
I had to exit MagicMirror to get back to the Raspbian desktop, and go into Preferences for display. There was an underscan box checked, so I unchecked that. After reboot, the screen was right-justified, with only a gap on the left.
Another post (https://forum.magicmirror.builders/topic/5318/remove-margins) tipped me off to edit the main.css to remove the margin (set to 0ppx), and that’s gotten left, top, and right all set. There’s still some space at the bottom, but it is past my bedtime. I’ll have to look at that in the morning.
Maybe this could help for you as well, hopefully. Good luck!