I don't think it's unusual for artists to feel anxious when they begin a painting. As Ann K. Lindsay, my teacher and mentor expressed it: "Art is our heart coming right out of us onto the paper, into the world; no wonder we feel so vulnerable...."
Below you see another way to make a color study. When making studies like the one above and below, I recommend using watercolor paper when possible. Watercolor paper will give you a truer sense of how the colors will look in the actual painting.
Now I'm ready to paint!
Common Yellowthroat sketch in ink and watercolor
Cornell on Common Yellowthroat