There's no shortcut, there's nothing you can take, you just have to keep putting yourself in the same situation over and over again. IOW, you have to develop your confidence. And confidence is something you develop based upon your past performance. If you've walked into the center of the ring and given as good as you've taken, you will carry that confidence out of the ring with you and it will be part of you in any future endeavor. But obviously, this doesn't happen right off.
Confidence starts to develop with the spark that propels you to compete in the first place. Truth be told, some don't have the spark at all and just spend endless hours practicing by themselves, playing for fun, never entering a tournament, or staying on their home table. But if you have the spark, as you seem to have, your first few times in the ring you're likely to go out on a stretcher (figuratively speaking

having taken the worst of it. This happens to all of us the first few times and it's during this period that one of two things can happen: the spark dies out and you convince yourself that you have no talent for the game -- basically, the experience is not worth the damage it does to your ego --- or you say to yourself, "I can do better."
You go over the experience in your mind's eye and examine not only what you did or didn't do, but also your opponent's performance. You work on your skills and you enter the ring again. I think this is the essence of developing confidence and a winning attitude: the willingness to take your lumps, do the work, and try again and again until you succeed. But, unfortunately, too many people want a magic bullet, a secret technique, and are not willing to do the road work that leads to winner's circle. Just keep at it. If you do you'll *earn* the confidence that comes from having the will to fight and lose, until you have fought and won.
Lou Figueroa