Social anxiety stems from the belief that people are going to judge or reject you. If you experienced judgement, criticism, blame, or felt dismissed as a kid, it makes sense that you expect to be judged or rejected now. You might have a harsh inner critic who points out every flaw before anyone else gets a chance. This inner critic thinks it's preparing you, but really it's undermining your confidence.
I teach clients to give themselves the security they needed in childhood. When you feel secure from within and accept yourself unconditionally, other people tend to follow suit.