Im a sophomore in high school and it is my dream to go to the Naval Academy. Last year my grades were not excellent (I got a C but the rest were as and b but I took all honorss) but this year I am full IB and I have gotten straight A’s so far and a 4.0 GPA weighted. Freshman year I played JV volleyball and this year I have not played a sport in school but I ran two half marathons. Do I need to play a sport this year? Next year I’m going to play cross country and try out for track. I have done volunteer work at an animal shelter, church, and the local homeless shelter and I am involved in Current events club, choir, and I am an ambassador at my school. I also started a neighborhood group that gets volunteer hours once a month. What can I do to help my chances at getting in?
Have you been nominated by a member of Congress yet? Do you have any diseases to note? Yes you should be varsity level in a sport. Not sure about Navy, but West Point requires it. Are you ready to serve in the navy for 6(?) years after you graduate? That C will hurt you, don’t get a C ever again. Try very hard to not get a B. You don’t have a good chance at all, because its Navy, no one ever has a good chance. Good luck, but have a safety school. No matter how qualified you are, there is always a chance to be denied.
I’m only a sophomore so I have not applied for a nomination yet. I do not have any diseases, I’m very healthy and like I said I have run two half marathons this year and have a third coming up soon. Of course I have a safety school, I’m aware that it is extremely difficult to get into! Thank you for your reply! 
I’m a freshman, and my dream is to attend the Naval Academy as well. Do they have JROTC at your school? At my school, we have Naval JROTC which I am in. You should strive for all A’s the rest of your high school career, and class rank is one of the biggest things the service academies follow. I have straight A’s all year, do cross country and track, on orienteering team through JROTC, and in one AP class to help my class rank. Good luck to you, and start writing letters to a senator or governor in your state.
I'm only a sophomore in high school as well and am by no means an expert on Naval Academy admissions. However, I do know two midshipmen (A MIDN 4/C and a MIDN 2/C) at the Naval Academy, have visited the Yard twice with my Scout troop, and attended an "admissions brief" where representatives from USNA went over the entire admissions process and what generally looks good on an application. Again, I certainly am not as qualified as an admissions officer or your BGO to give you advice, but I'll just tell you what I learned.
First, honors and IB look good, but only if you make the grades. That means as many A's as possible. One admissions officer said to shoot for at least a 3.7 cumulative GPA, but even making that isn't a guarantee for an appointment, as Congar said. Even though you got a C, it's not the end of the world. It only means that you have to keep getting those straight A's like you are to show that you really are committed to academic excellence.
Second, being active in sports is very important to the academies. So yeah, play a sport every year, preferably every season. Even if it means only being JV , playing a sport shows you are dedicated to maintaining your physical fitness and that you can work in a team. That being said, strive to letter in Varsity for the sport you do. It's something Admissions Boards like to see.
Third, your EC's look strong, but there's always a way to make them stronger when applying to one of the Academies. The mission of the Naval Academy is ultimately to graduate leaders capable of handling the rigors of military and naval command, and its preferred that you are already familiar with leadership. This leadership can be in your student government, class council, or the club that you are in. If you can, try your best to earn a position of leadership in whatever you do, no matter the size of the organization. Your volunteer work is very admirable though, so just keep doing what you're doing with that.
One more thing to keep in mind: chances of admission are greatly affected by where you live. If you live in a place where there are a lot of people vying for nominations and appointments to the Academies, focus on being the best in your class, the best on the team, and the best leader you can be. However, if you live somewhere that does not send a lot of people to the academies, that doesn't mean you should let up. The Naval Academy is a mentally and physically grueling place for those privileged to attend, so preparation is key.
I hope the information I could give you helped. I suggest you visit the USNA website for more information on what the application process is like and what you should be doing to become a competitive candidate for an appointment. You should also join their mailing list so you will be notified when there is an "admissions brief" event in or around your area. I wish you luck, as both of us will be starting the service academy admissions process in a short time.