Pictures or details of your setup will help us help you. However, chickens innately know more about incubating and caring for chicks than humans ever will. They need little or no intervention other than access to food, water, a place to defecate and dust bathe.
The hens do all the work.
My best advice is to interfere as little as possible. Don't worry about counting, candling or anything else. Many people love to intervene and even insist it is necessary. Don't listen to them. Hens have been hatching eggs longer than humans knew chickens existed. They didn't need human intervention then and they don't now. Let her do her job and you'll have better results.