I did this on our trip last year but did not know to stop at the hotel and check in first, when we went to enter the park our bands didn't work so they sent us to guest services, were able to check in there in a couple minutes and then go to the park. They also gave us a free fast pass for our troubles.
Go to the hotel first if you can, if not, you should be able to do it at the guest services window at the park.