I have since purchased an X-acto knife and bought some real drawing paper that is the right size, so I don't even have to really trim the paper. I feel much smarter now. I think the knife went a little deeper than I originally thought, but the wound is healing very nicely, and I have only a nominal bruise to show for it. Fortunately, that accident wasn't as stupid or bad as another knife accident I had while trimming a Ficus Tree with a serated bread knife. That one wasn't pretty at all, and I still have nerve damage.
Someone should ban you from using knives! I only use paring knives because my left handedness gets me into trouble!;-)