Depending on what time you arrive on the 27th you may not make the B.C. We have done the B.C. a few times and it is a blast! The entertainers on the B.C. are amazing and get everyone involved in games (if you want to). Basically think of it as a floating version of the resort with a bunch of booze, drinks, hilarity and a great way to interact with your fellow resort goers.
My wife is a little shy also. We both arent as open as some couples but we are open to witnessing anything. It's not all super models on the BC if you know what I mean. Lots of fit beautiful people on the cruise and a fair share of big beautiful women. The party does get a little wild. Wilder than we normally party. You might see BJ's or even couples having sex but that's minimal. We partied a played a little on our first and only trip and didn't feel uncomfortable at all. The girls must take their tops off shortly after departure and they hang their tops on the boat like a flags. The BC is a lot of fun and there is no reason to be shy.
We arrive on the 26th for our fourth trip to TTR so we will be poolside when you arrive the next day! Cheers from Canada!