Definitely take the sat also if you can. Some people do better on one test over the other. And yes, the academy does super score. This simply means that they don't take one test sitting as a whole. Meaning, they look at each individual subject test separately and use the best score of all the times you took the test. In other words, your individual test score can never go down. If you took the test 3 times and your best math score was the 2nd test, they'll use that score for math; and they'll use the first science score if that was the best, etc.
As for your competition, realize that you don't have just one set of people as your competition. As a minimum, you could have 2 sets of people you could be competing with. Some people could have up to 4-5 groups of people they are competing against. If you only have 1 nomination, say your district representative, you will compete against 9 other people on that slate of nominees for 1 appointment. If you don't get that appointment, you may be competing against 9 others if you also had a senators nomination. If you don't get the appointment for that slate either, you will eventually go into a national pool along with all the others who didn't receive an appointment from the slates they were on. The national pool will have a couple/few thousand people in it. These then become your competition for a remaining 500-600 appointments.
This is why it's important to get as many nominations as possible. It's like having a lottery ticket. The more tickets you have, the more chances you have. But the competition chances. You could be the second best on your districts nomination list and didn't get the appointment, but in the national pool, you could have 1000 people with better scores than you. This is also why the academy looks at the whole candidate. Not just gap, not just act/sat, not just sports, leadership, volunteer time, etc.
So all you can do is the best that YOU can do. You can't control your competition. Don't worry about things you can't control. Get the best gap, act/sat, etc. that you can do. Make your application/resume the best that you can make it. There will always be someone better than you at something or some part of the application. Again, the academy looks at the whole candidate.
Unfortunately, having wanting to attend the academy or it being your dream, doesn't matter. Your desire only carries a small amount of weight and that's only recognized in things like your alo interview. And the academy is never what you thought it was going to be once you get there. Even if it's something you say you wanted your whole life. I can't tell you how many cadets quit the academy who were at the top of the selection and who wanted it their entire life. They raise it wasn't what they expected. Best of luck.