How do you have confidence?

I’ve been in scholars for a while and benefited, and still feel like a newbie.
Some things I’ve learned and overcome include: Taking immediate, imperfect, decisive, massive action – believing that it will happen even if I don’t know the how, and that “they don’t have to understand, I do.”
These tools have allowed me to build a new website, create a training course in my field, market it, and be ready to launch it tomorrow morning. However I’m terrified. Excited, but also terrified. People have signed up who are experts in the subject matter, likely way more than me. I’m building everything now. Each day I’m creating materials.
I feel as if I am a complete fraud. It feels like a strong case of imposter syndrome – and I don’t often have that (maybe don’t push myself enough???).
My question is how do I feel confident? I’m guessing the answer would be to put it in an intentional model and determine the thought that will grow confidence – I just cannot think of a single one that I would believe and would grow confidence. The best I’ve come up with is – well, if it’s a complete fail then at least I will have learned something.
Then I think how the 30some people who signed up are part of my community, and what if I let my community down. What if they go from thinking I am great to thinking I am a sham? What if it goes terribly, I do learn something, and then no one will sign up again?