If you did the reservation online, be sure to print out the document showing your room reserved at that rate. If they should try to charge you more, the documentation should resolve the issue quickly at the front desk. If not, I would ask for a manager and if that fails, dispute the charge as an overcharge.
It probably won't be any problem at all, but I always like to have a hardcopy of everything just in case. I was very concerned a couple of years ago about a long National car rental. I just knew we would return it and they would try to up the price (which was already about $1000). When the young man at the checkin gave me the receipt, it matched to the penny the cost I had seen on the internet.
Sheila