Enjoy the trip. If you haven't planned your days yet or are open to suggestions I highly endorse Tulum. It's about 90 minutes south of Cancun and really beautiful. Great beaches, hotels (small kinds) and awesome food.
After my trip there last year I sent a few groups of friends who either spent their entire time down there or just a night to get to see the beach, ruins and sinkholes.
We stayed a Be Tulum. The hotel was great, service beyond expectations, nice beach and damn the hotel had a good bar and restaurant.