Well dang. Oh well.
Don't blame yourself for doing something wrong. It takes a few tries at incubating to know what you are seeing. I think it's more likely that the eggs were the problem. So many things can happen to them BEFORE they get in the incubator. If they were fertile then they could have gotten chilled before you received them. Or they may have been handled roughly which would detach the blastoderrm from the yolk. The egg would then have no chance to develop.
You still have plenty of time before school is out for the summer. Find some fresh hatching eggs from someone locally and try again. Hatching can be a wonderful learning experience for the kids.
I got the everything locally, from a hatchery near me. I went back into her barn with her where she had a bunch of brooders and the eggs were sitting on a shelf nestled in foam. She told me to let them warm up for about 6 hours before I put them in the incubator.
Maybe I'll see if I can find a good affordable incubator on amazon or someplace (since this one was a rental) and find another place with eggs and try again. You're right, there's still 3 months until school is out, we can keep trying!