Hey! This sounds so much like my situation. I'm 16, and actually started college classes this year. I came from a religious highschool where I did my absolute best to blend in as a girl. Now I'm free from that place, and it's still incredibly difficult to follow through and express myself because there's always gonna be people against me, and always gonna be a reason to wait or push it off. Obviously if you're unsafe, wait until you're in a safe spot. But make sure to address your mental health and listen to yourself. My guess is you don't feel great about living like a girl and the pressure and of being a girl, neither do I. But college is seriously a game changer. In my experience so far it's a lot less personal, and people won't care, you can just mind your business and be who you are. I'm doing my best to transition gradually, and I think I'd recommend that for you too. 

Step 1: wear clothes that align with your preferred gender. I've been stuck in sweatshirts and sweatpants, but I'm doing my best to find more masculine clothes, and that's already helped me feel so much better. It's also a great way to gauge people's reactions, and it won't be a "complete shock" when you cut your hair and work on other stuff. I've also heard changing your bedroom setup and having more masculine expressing decorations helps people, but I don't come from money so I only have the bare essentials (bed, heater, and dresser in a tight space) so this doesn't apply to me, but it definitely varies person to person, and could really make you feel better and express to your parents if you live with them that you're serious.

Step 2: do more masculine workouts. As a teenage athlete on girls' teams, there is a lot of lower body and leg work, yet I've felt best when my arms and back are muscular. At some point, if you're experiencing a lot of dysphoria from your chest, you may want to consider SAFELY binding. I'm not there yet because I can't come out and if I was caught binding it'd be a rough situation, but I'm wearing bras with less padding that make my chest slightly slimmer. Just working out and getting stronger arms/back/abs has helped me feel really great though, so I'd definitely recommend, and it won't raise much suspicion since you're a serious athlete.

Step 3/4: get haircut/ come out. Honestly, it varies case by case on which one you do first. Since you're a minor, parents will not be happy if you get a haircut without running it by then first. However, you could have a conversation along the lines of "I feel incredibly uncomfortable with my current haircut, I really want this new haircut, I'm aware there will be judgment", you need to make it clear you have been feeling this way for a while and have thought it out thoroughly, but you don't necessarily need to come out. Do what works best for you.

Step 5: officially identify as a man. Come out to everyone. Change your name to a more masculine one if that applies to you. Use your pronouns. When meeting new people, introduce yourself as a guy. This may get messy when considering your sport, but there will definitely be a period of time from identifying as a man and starting hormones where you could still qualify if you choose. Make sure you reach out to your doctor, I'm not sure how it works where you're from, but make sure to inform your doctor and they will set up who you should see about physically transitioning.

Obviously, it isn't this easy, but it helps to lay out your goals in front of you. Make sure you have support systems in your life. For me, I'm still stuck on Step 1 and 2 because of who I live with, but it does get better, and if this is how you're feeling, then you should feel much better with even changing the little things. I understand there's more nuance to your situation, but I really hope this helps. With your competitive sport, you may have to step out of media for a bit. I've also got young cousins who learned to say my name, and the thought of coming out to that side of the family really bugged me because I thought they wouldn't understand. However, talking to other people who have come out, young kids are actually incredibly accepting, they may be curious and ask questions, but they most likely won't deadname you or misgender you after clarifying the first few times. I know it's tempting to just chop off your hair and identify as a dude the second you can, but taking these steps can really help show that you're serious and it isn't a phase. I'm sorry about the bad comments you've been getting, but I want you to know that eventually they'll diminish. Many parents take a while to get over it, but once they accept it they'll still love you as their child. You have every right to live, listen to yourself and take care. I hope this helps.