Feeling nervous at bigger jump heights

Feeling unsure when you take on something new, like bigger heights, is completely normal. You mention that single fences go well, but that you get frightened once you are on a full course. My tip is to build up gradually: jump one fence at the higher height, then add a second, then a third, rather than putting up a whole course at once. It is no surprise that your horse picks up on your nerves either. He is paying attention to you, which is actually a good thing. Think about how you ride, and what you are thinking and feeling in your body, when you jump heights you feel safe at, and see whether you can carry that across to the new height. It might be focusing on how you hold the rein, or focusing ahead to the next fence. If your horse recognises your riding from the lower height to the higher one, he will feel secure.

Good luck!