As much as I chastized myself for being stupid, I actually managed to get away with it. The two remaining co-op students that I had made offers to accepted the offers. That means that I didn't have to be in the unenviable position of retracting a rejection.
I could always use this lesson as a positive. After all, I did choose 3 co-op students even though I only needed 2. That means that there was a little bit of wiggle room available. Some would call that good planning.
Others would say that sometimes it's better to be lucky than good.