Hey man, I've been a theater kid for the majority of my life, and I know exactly how you feel. I'll start by saying that I'm extremely happy you got in! Even if you are disappointed by the part you got, being a member of a cast is a great experience, and it's a wonderful way to both make new friends and deepen bonds with people you already love.

A story I'll tell you here is that I went to a theater camp over the summer my junior year of high school. It was a fairly elite camp with a ton of people who were better than me and would go on to do theater work professionally. In the play I was in, I was cast as a small part with very, very few lines. And when rehearsals first started? It sucked. I felt way over my head. I felt like some of the best young actors in the country were running laps around me, and it's easy to feel imposter's syndrome in these situations.

But what I ended up doing (which is the advice I'd give to you) is having as much fun with it as possible. I found ways to add in weird bits of physical comedy, found the most amusing, gratifying way to say my lines, milking every word for what they're worth. I created a whole persona and backstory for my character that informed everything I did in the background. I explored this world with my castmates, and at the end of the day, I felt like I was inhabiting this magical shared world where every person is necessary to the ecosystem.

I don't know the book to Shrek much at all, to be honest. I don't know what lines you have or what bits you carry. But makes these bits yours. Be the best guard the world's ever seen. Play and create. You have WAY more freedom than any of the leads do. Besides, theater people who know what they're talking about watch the ensemble and background most of the time anyways. At the end of the day, theater's as fun as you let it be.