Don't Defeat Yourself...
I am afraid that you are already getting on the wrong path here. You are already worrying about things that you cannot control. The number of nominations allowed, competitive area, that the other candidates are better than you, etc. If you peruse through a lot of the advice given out on these forums, you will realize a common theme...don't worry about what other people bring to the competition (SA appointment is a competition, make no mistake about it!), but rather make your personal package the best that you can and most importantly, that it is a reflection of you as a person and what your strengths and weakness are and what you can contribute to the OFFICER pool! Do not fall into the trap of enhancing your candidate package with ECAs that you are not passionate about just because that is what you think the admissions board wants to see. They will see through all that. Even if you get away with it, can you maintain the farce for 4 years or throughout your military career?
Make your candidate package a reflection about your beliefs, your passion, what you think is important in a leader. Bolster it with your memorable and personal experiences and more importantly, show them how all of these experiences have made you a better person and possibly a worthwhile leader. With that in mind IMHO, grades, GPAs, SATs, ACTs, ECAs, leadership positions, awards, recommendation letters, sports activities will all follow you and help describe you as the person of character that you would like others to see you as. Do the best that you can and that in your heart you have given it your best shot.
A wise man once said...
If you cannot do something about it, why worry?
If you CAN do something about it, why worry?
In other words, between now and the day you get your Appointment Letter (or your rejection letter...), you have to leave out useless verbs such as worry, regrets, doubts, etc. as they will do you no good! The least that you can get out of the admission process, irregardless of the outcome is that you have a better understanding of yourself and what you are capable of!
Know Thyself! (Socrates...)
Good Luck!
GO NAVY!