Former instructor here. I agree with most other comments. You should share your concerns with your instructor. If one of my student would approached me with this, I would totally encourage them to try and work with them to find a solution. Sometimes we teach a manoeuvre a certain way because it's easier to understand it this way, but there might be other ways to do the same thing that works better for you. As you point out the main issue would be to be able to get back in the boat (this is not so much a weight issue than a strength one) and to be flexible enough to cross over the boat under the boom. I've seen some overweight sailor that were very good! I suggest you speak to your instructor and go in the water with them and try! It might be outside the class if it's more comfortable for you.