Don't feel bad Lislee, lots of folks are fooled by the advertising of rainforest, mayan ruins and things like waterfalls when they plan their trip to San Pedro/Ambergris caye. Those things are on the mainland. San Pedro/Ambergris Caye is snorkeling, diving , fishing and sailing, a flat barrier reef island for island kinda stuff.
Most of the mainland things can be accessed from the island but are a day trip and a few would have to be overnights.
Lots of tourist split their vacation half on the mainland and half on the islands. We call them Surf and Turfs.