Did you count the day you set as day 1 or after a full 24 hours of incubation?
Have your temps been OK during incubation?
21 days is just a guide, some hatch earlier and some hatch later. Each chick is individual and tend to hatch when they are ready. I'm afraid they don't think about the worry they cause!
95 - 100 is a big variation in temps so they could be late as enola has said. Prolonged low temps can also cause development issues with chicks. As you counted day 1 as the you set you are a day head of yourself. Day 1 is counted after a full 24 hours of incubation. Say for example you set the eggs on a Monday day 1 would actually be Tuesday. Day 2 would be Wednesday, day 3 would be Thursday and so on.