Even with your Dremel on low speed, you’ll occasionally get a nice big chunk of plastic that builds up under the cutting wheel. After you get done cutting one line, wait for a few seconds then you can usually just carefully grab the little plastic chunk and break it off without destroying the cutting wheel. The cutting wheels are inexpensive, so no worries there, but they are annoying to change out. Not hard, just annoying.
Now also notice that Jeff is picking/peeling off the bits of plastic that are still around the edges of the hole. This stuff almost always comes off without any trouble. Just grab and pull, or use a plastic knife or such to help break it off. You are like…almost done at this point!