I am sure you will have a great time. Get involved with the staff at your hotel and the things they organise. This will be a big part of enjoying the holiday.
Dont listen to the rep who will tell you to only buy trips of them, and that you should never book with people off the beach. You will pay almost half the price if you book on the beach. I have ben on a waterfall trip that you might enjoy (although i dont know your age / likes or anything), for about 30 dollars you go out in an open top jeep to see a few sights before climbing up 7 mini waterfalls and then sliding back down them.
Go out of the resort and use the transport on the main road to get to Sosua and Caberete. Also, haggle with everyone because you do not need to pay the first price you are quoted! Be careful not to pay over the odds!
You will probably arrive in Playa Dorada as i am leaving, haha.