I’m new to yoga as well and I’m very overweight (I’d like to lose 60 lbs).
I’m definitely the biggest person in my class but that doesn’t stop me from doing well. Your size is not all there is to your fitness level.
I am hard on myself when I can’t do some of the poses, but I never quit. The hardest part as a beginner is learning to do the poses as correctly as possible. I find myself looking around to see how to do it… which is distracting to me. I’m looking forward to getting more comfortable with the poses so I can concentrate on myself. I go every other day and have noticed less back and shoulder pain.