I know you've already had your show but for future shows:
Keep calm. If you are calm then you will be less tense and therefore less likely to mess up. Also, block out the judges and any spectators, just imagine it as an afternoon when your practising. Think to yourself, the last time I practised I didnt have any problems (if you did try and correct them before the show) so why should I have any problems now? If your horse can, jump a tiny bit higher than the round you're in so you can think to yourself that you know you can jump this. Also make sure you know the course like the back of you hand and make sure you know how mnay strides your horse should take. One of the most important things, your horse. Make sure he is fit and healthy and give him extra care and attention before the show. Even if he messes up reward him at the end. Your horse is the one that has to do all the jumping so be grateful. If you treat your horse well and with respect he will treat you well and with respect. And last but not least......Enjoy yourself!!!