If you know that you were monitoring the temps and humidity throughout, and nothing crazy happened then I wouldn't worry. I've had them hatch on day 20 and then some on day 22-23 before. Watch for the signs of life/hatching preparation like others have mentioned and just be patient--which is so hard I know! Good Luck!
I am a first time hatcher and we are on day 20 today. I have one egg that is moving, it is a very subtle move so you really have to watch for it. I was surprised to have movement today, but I guess just like kids every chick is different. Good luck!