You need to work on your mental game. The skills are the same in practice or a match, so why do you shoot different? Mostly it's artificial pressure that you place on yourself. Pressure to do well, pressure to have your peers see you as a good shooter, pressure not to fail. When you step up to the line, you need to be confident in your abilities, you need to believe that you will win, you need to be positive. The only stress should be the drive the win.
If you have any doubt, that is what the mind will focus on. Your mind will force you to make the mistakes. Think you will miss a target and you will. see another shooter miss a hard shot, you will focus on it. Know that the other shooters mistake will be a mistake you can take advantage of because it is one you will not make.
Shooting is very mental and it is the hardest aspect because few really work on it, but having a strong mental game will be the biggest factor in consistently doing well