I am an imposter!

So last night I had my first rehearsal for the benefit Christmas concert I am performing in. The concert is for Standing O Productions, an up and coming theatre company in Annapolis. I am very excited to be working with this company for the first time (I was cast in a previous production but had to bow out due to an unavoidable commitment). The company is run by my friend Ron, he has already asked me to co-direct a project with him and they have had a very successful first season.
All of this being said....I am an imposter! Yessir, I have no right being onstage with any of the people that are in this Christmas concert.
What? Why, Sara? You are a singer, you have always sung, why should you not be allowed to sing amazing choral, Christmas music with these folk?
I'll tell you!
These people are fantastic! They can all read music and sing like they've known the song their whole lives after only seeing it once! They are all vocal music majors and choir teachers and paid performers! Oh my! I won't lie, I held my own, but shit, we sang through 'O Magnum Mysterium' once(!) One time completely acapella and we were right on pitch! That's hard to do kids!
I looked around the room at one point and I felt like a kid being moved to the adult table for the first time. I mean, I have seen these folks, some I have performed with already but damn.
Ok, I know you'll say I'm being too hard on myself...I was asked to do this so I must be doing something right...right?
Well, I can't read music, never could. I've always had a good ear (thanks Grandma) and no matter how much I've smoked in the past I still seem to be able to hit ridiculously, unnecessarily high notes.
I tried to be a music major for about ten seconds in college...do you know what music is people?...It's math. It's math and I hate math.
And yes, I have gotten paid to perform in my adult life. In fact, in Chicago I actually got to sing for a living for almost 2 years.
But I still felt kinda small. At the beginning of the rehearsal the director (out of Baltimore, a man I've worked with once before) said, "you can all sight read right?" ( I assume he asked this because we have a shitload of music to learn in not at all a lot of time) Two of us, not so sheepishly, raised our hands and said "Heeeelllllll no!" But once again we held our own.
I am pumped though. I actually have some family members coming to see this and I am already very proud of what they will see.
At the end of rehearsal last night we were finishing up and the director, who is a music professor at a local Baltimore university and graduate of the Peabody Institute (fancy for "knows his shit") said to all of us that he had "more fun in three hours with us than all semester with some of his students"....
I guess that's fancy for..."we sang the shit out of it!"