I remember feeling like that before getting my horse. I only had lesson horses to ride, and lots of people were coming to the stables with ribbons and stories of how fun the show was.
If you can't ride in the show, give yourself a job to do at the show. Be the official video taper or be a groom for one of the riders. This will put you in the middle of the show and you will be making a contribution aswell as having fun and watching people ride. And by doing that, once you get to ride in the show, you will know what to do and what to expect.
I'm sorry that you had to sell your pony, but don't worry! A horse will come along that is just right for you at the right price! =D