Carrie, you will absolutely LOVE the catamaran group outing!
Honestly, my wedding day was the best day of the trip, but the private catamaran outing we did with (@80 ppl) - was the SECOND best. You will not regret it! The catamaran we went on took us to swim with the dolphins, snorkeling and to Cayo Blanco (a pristine island) for a big lunch. There were other catamarans (meaning other people) on the island but the catamaran and dolphin time was exclusive to our group.
It was amazing, and once you go you'll agree that it is the best money spent!