And never assume a course is closed just because the organizers say it is. In your first races, just compete against yourself, and against the course. You want to do as well as you can, but don't pace yourself based on the other riders. Pace yourself based on your experience doing hard rides at that length. Otherwise, start at your regular riding pace.
People get so excited they tend to ride over their heads.
You don't win races on downhills, usually. You win with consistent riding. When it's over, look at how you did. If you identify your weaknesses, you can address them. Do the same thing for your strengths.