You got the gig because the people in charge, the client, the buyer, the booker, the agents all thought you should be the one up on stage.
So why do you get up there and still doubt you should be up there?
It’s not a great habit to lean on what strangers think of you to give you confidence…but feel free to remember the truth of the situation. The truth is everyone surrounding the event believes in what you’re doing enough to put their professional reputation next to your talent and skills on stage.