I'm 6'3" tall and weigh in at about 360 pounds. Very little of that is muscle. I have a big gut and it gets in my way all the time. I am tired of it but don't seem to be able to do anything about it.

I can tell you from experience that it helps to have a good attitude. When I am in a good place in my head there isn't a person on Earth who can shake me. That hasn't been the case lately but I'm getting back there.

Be that as it may, singing on stage is one of those places where you are easily cowed by others. You can't let that happen. You know you have talent and you know you can perform. Other people may have opinions but those are not yours and what they think can not hurt you unless you let it. Be yourself and know that you are pleasing the one person on Earth who really matters, you! The rest of us are secondary.