Man, you poor thing. :( It really makes me angry and upset for you to have to go through what you did - and for no reason at all.
I have empathy for you for having to be in a highly competitive barn. When I lived in GA, I boarded at a very competitive barn as well. 95% of the boarders had a large amount of money that liked to flaunt it and act very snobby. I of course, wasn't the one with the money so me and my cheap little gelding often felt intimidated and embarrassed to ride. My horse is priceless to me but the competition was so fierce I often forgot that it was meant to be "fun" to ride.
Anyway, I'm away from that barn and am back in the saddle full force. I am very happy to hear you have gained your confidence back. You're obviously a very strong person - I'm afraid many riders in the same situation as you would have permanently lost their confidence about riding. To say you are back in the saddle and jumping again is a huge accomplishment, pat yourself on the back!
I also have past shows that in a sense haunt me - I was put in situations I didn't want to be in. However, I'm having to come to terms with the fact that the past is the past. There is absolutely nothing I can do about the past but learn from it and move on. The only thing I can control is this very moment. I can make the conscious decision to either dwell on the bad moments of my life or I can keep my chin up and move forward happily. Try keeping this in mind when you feel overwhelmed.
You've been taught to put a very large emphasis on shows I assume. This would make anyone feel overwhelmed. I think the key to your situation is to realize that shows are not a huge important event. They are simply a different location to ride. It you make them out to be a huge deal, they will be a huge deal and you will feel utterly overwhelmed. However, if you realized it is just a change in location and a very simple thing - things will be far less scary.
So, are you ready in your training? Is your horse ready? Are you, as a RIDER, not a competitor, ready? Do you need to do anymore flatwork or jumping exercises? If you believe that you, as a RIDER, could successfully complete the jumping course at home, then sure, go to the show. Because you are obviously ready, you are just putting to much pressure on yourself.
If you still have doubts, is there any way you could go to the show and if you feel like you can't do it, you could just hang out and relax?