In almost two weeks, I'll be on different back to back repositioning cruises (RCI) that stop at a lot of ports. So, I've been stressing a little on what excursions to take also. I booked the Tulum and Xel Ha excursion which I'm not worried about at all. I cancelled a Rhino Rider excursion because I was worried about the weight limit. But then I booked a parasail excursion because my husband (who isn't fat) didn't want to do it without me. I'll let you know how it goes if I get back before you.
I've only been on one cruise so far, Carnival Holiday, for the 4 night to Cozumel. We went to Chankanaab and swam at the beach. I didn't feel uncomfortable there. I wear skirted tankinis or swim short coverups over my swimsuit. I know my upper arms look awful, but that's the only time they get to see the light of day and I don't like to swim in teeshirts. You should go for it and get in the water. Don't waste your valuable vacation time worrying about what other people think.