As you have many points, I will go through them individually, in order. First, I understand what it feels like to only have one friend (or even fewer). It can be difficult to feel supported with only one close friend, especially when they are busy. However, she cannot know that you need her support without you confiding in her. Try finding a moment when she can listen (such as at lunch) and you can both vent to each other. Be sure to listen to her struggles as well.
As for your phone, being grounded for so long for something that is seemingly a minor offense can feel harsh. Try having a real conversation with your parents and discussing why you have been grounded for so long. Suggest something you could do to earn your phone back. During your talk with them, you could also ask why they do not trust you with driving. Nobody is good at driving at the start. That’s why someone teaches you. If they cannot trust you to drive, then ask them to go on a drive with you on roads that usually have light traffic and they can instruct you as you drive. Let them know that you feel as if they are not proud of you. Give them a chance to listen to your points.
This year, I think you should go easy on yourself and take a break from Color Guard (as you have been doing) and find out who you are and what you need. Then, join the Color Guard again next year and reunite with your team if you then feel that it is the right choice. Overworking yourself can lead to worse issues, such as "fatigue, hypertension, difficulty concentrating, irritability, changes in appetite, insomnia, headaches" according to Psychology Today. Getting a B here and there is not the end of the world. In fact, it could be good for you. It means you are being challenged academically, but you are still trying your best.