Sounds like he may have gotten stuck while trying to zip if he's been stuck there for two hours. Helping with an already started zip is usually a very easy/safe assist if you are willing to intervene.
Carefully break a little shell along the zip line, check for bleeding and quickly stop it with a clean paper towel or cloth if there is any. If there is bleeding put him back in the incubator and wait for awhile before trying again. If there is no bleeding continue chipping off shell along where he would zip until you've made it all the way around the egg. Once all the shell is broken he/she should be able to push out. If after you've finished the zip he/she looks to be trying to push but is struggling it shouldn't hurt to pop the top off yourself. He/she should then kick out of the rest of the egg when ready.
Good luck, hopefully you'll have a healthy fully hatched chick soon!