You won't be scared for long. Being that you don't have a lot of experience, I'd call your reactions pretty normal. It is scary the first few times out. I get overconfident on the rivers I paddle a lot, but when I paddle something I have never or seldom run I am much more cautious and I get coffee grounds in the stomach kind of feelings.
I think the butterflies will go away if you choose to stick with it. I would try the same runs on your personal time when you don't have the pressure to perform in front of employers and customers. I haven't commercially guided, but I love to take paddle teams of new people down local runs. I am always a little more on edge with those groups because I care about them and they don't know what I know.