Take the plunge. I think everyone on this board and everyone around the world has seen someone somewhere in a bathing suit that didn't have a model's body. My husband has a Dunlap body (the stomach "done lap" over the belt) and he's out there in his bathing suit. My father is 78 years old and he wears a Speedo (I know, it should be a SpeeDon't but he's 78 so I don't argue with him, just pretend he's not with me).
As far as your stuff, we always just put our shoes and T shirt on the ground somewhere (so we don't occupy a chair if we don't need it) and then put the room key under the shirt. We figure that no one really wants a potentially smelling T shirt and who the heck wants to take someone else's shoes? It's not like you'll be wearing a designer label to the pool (well, maybe some do). As for the key, you can always get that replaced (it's a hassle but you can do it) and there's no room number on it anyway.
Relax and have fun.