Next time your horse refuses a fence instead of feeling negative ab=nd loosing confidence, be determined to jump the fence to the best of your ability.
Insted of thinking about getting around the course think about every fence, as you are going over one start planning your route for another.
On your approach sit deep into the saddle keep your leg on no matter what speed your horse is going at but half halt at the same time so that you have a shorter canter stride, this will make you feel more in controll, and it will also give your horse more scope, about 1-2 strides before the jump let the canter strides get a bit longer so that the horse does not think that you are pulling it back, this will also give the horse more confidence.
When learning the course plan out all the things that could distract your horse, don't be afraid of them, just aware that they are there so you may have to put a little extra effort in.
It sounds like you should also go to some smaller shows and jump smaller than normal, this will help with your confidence.
Hope this helps