Your score is always what it should be...
... because it is what you scored.
The champions score better because they harness the energy and focus it into performing better.
The shooting part is the easy, the rest is hard, especialy when you know you have to be near perfect to win when there is real competition around.
Practice is practice, no one shot to win, matches you get one shot to do it perfect. There is a difference, but at a certain point you have to treat everthing the same. Every shot you take is just as important.
If you've been shooting 18 months and think you could walk away with most matches, you might need to re-think where you really are. There are lots of shooters who've put in a lot more time and energy than you could have possibly done in 18 months. Not to slight you in anyway, but there are so many shooters that just have tons more skill and experience out there, so maybe think about the fact that they might have skills that you aren't even aware of yet, and keep pushing the limits. Just because you don't see them everyday, some will show up at the major matches and the results don't lie. They have the same amount of stress to deal with, and they know that it is each shot that will either break them or make them.
Experience each shot and forget about what everone else has done, or is doing, and you will perform to the level you are capable of at that moment in time. It is a never ending journey, because people are always raising the bar.