I started playing 2 hour shows with just 5 songs in my repertoire. I had never produced a single song when I was hired to record a singer songwriter's music, and I had never toured until my first tour with a rock band just after high school.
Truth is, I have rarely been qualified to do what's asked of me.
And the thing is, nobody is. No one has ever done something until they've actually done it. You don't know how well you'll do on that gig, or how tight your mix will be.
So don't be afraid. It's everybody's first time.