You’ve gotten some great ideas to help you out and the winter to put new patterns (of thought) to practice.
Another suggestion is to really look at what’s happening when you get nervous. What thoughts (all of them) are coming up? Afraid of failing? Messing up? Afraid if not looking, knowing, riding well enough? Fear around your horse? Fear of what your instructor might say? These are just examples, the list goes on. Once you’ve identified what’s happening now be clear about how you WANT to feel in the ring. In control? Proud? At ease? Breathing? You determine the state you want to be in, the relationship with your horse.
Next, list what’s already going well. Instead of beating yourself up or worrying yourself into a tizzy, breathe and picture what you and your horse are already good at doing together. How does that image feel? Practicing riding those feelings in your mind is very beneficial to building your confidence.
Now, practice riding in your mind the way you WANT to feel. Notice how it’s easier since you’ve practiced riding the good stuff you already do?
Now take it to the ring. Whenever you feel those negative, nervous thoughts or body tension come into your riding, breathe, and go back to the positive feeling/sensation you’ve been practicing. Ride from there. You’ll notice and change your pattern thousands of times before it becomes the new normal. Stick with it. If you can train your body to ride, you can train your brain to ride with confidence. When nerves or fear come up, you’ll have tools to work with and improve your experience every time.