Time to Finally Vent That Rage
Now you can finally reach for your hammer and go to town on the drywall. Yank it away from the studs (the slats of wood, typically 2x4s, that form the skeleton of the wall) until you've removed it up to a point relatively close to your scored line. Slow down, and stick to following the line so you're left with a nice clean edge.
Then you'll want to take a saw to remove the studs themselves. Be careful when encountering nails -- tetanus is not cool. You don't need to Google that, just trust us. Oh, and be careful with, you know, with that saw, too. Because it's sharp and all that. A reciprocating saw works good for both creating a straight line at the edge of the drywall and for removing the studs, along with the framing.