When I go to the gym, I'm the heaviest person there (I go to a women's only gym in town, and it seems like all of the members are these frickin' AMAZONS!). But the one thing I've noticed is that the other women in the gym don't even look at me when I'm working out. If they do catch my eye if I'm going to the dressing rooms, they give me smiles and looks of support, because at least I'm up and trying to do something about the weight rather than hiding from the world.
I know how it feels to be self-conscious about something like this. It's no small matter. But the self-esteem boost you'll get from actually accomplishing it will take care of any lingering doubts in no time at all.
YOU CAN DO IT!