I'm overweight too, and have been on and off since I was about 8. Fortunately, I was able to weasel out of certain embarrassing things (having to show my belly for abdominal assessments, etc) by volunteering for other things. I can't imagine that they didn't have a larger blood pressure cuff for you; that is really awful on their part, not to mention embarrassing for you.
I will tell you this though - working with overweight patients, who have those weight issues on top of other medical problems, has seriously motivated me to lose weight. I have lost 25 pounds since starting nursing school. It scares you straight, but also the stress kinda makes me want to binge eat all the time. Nursing school is crazy.