And if you're trying to books a third person after the original reservation then you should call the resort directly...not just show up at check in with an extra person. That person just might find themselves with no place to stay.
Actually I remember doing that exact thing karen. Me and my freind had booked ( dbl occupancy) then my other freind decided she would join us after we had already booked. So she went ahead and booked her flight with hopes the hotel would ok her to stay with us. We had to go through our travel agent though, and she made the arrangements with the hotel. I know she had to wait till the monday cause there was no amanager in on the weekend :?