What helped me when I showed was to imagine that I was only riding in front of my instructor and my cousin (who were both there, and have seen me ride, many times before). I also reminded myself to take deep breaths and that the main thing was to have fun. I was still pretty nervous in my first class but by the second I was mostly fine.
I advise you to remember that the more you worry about forgetting a course, the more likely you are to forget it!
I've never jumped in a show setting before, but here's how I remember my courses in lessons: colors and technical terms(?). Not sure what you would call it, but here's an example: green line to red oxer, then blue vertical, to pink bending line, etc.