Accept that things will go wrong. When it’s your fault, take the blame, fix it as best you can and apologize. Don’t let it happen again, but don’t beat yourself up over it.
Accept that there are going to be challenges, that you’ll need to do things you’ve never done, learn things you’ve never understood. But you’ll learn them. You’ll work hard at it and, as long as you didn’t promise the insane, you’ll get it done. And if you can’t, hire someone who can and relax.