Honestly, I think you’re wound up way too tight about this. A B+ isn’t going to keep you out of college, and burning yourself out with summer classes plus test prep isn’t going to get you into a whole different level of school than you could otherwise get into.
1 best idea is, work with a counselor/therapist. The vibe/concern that I get when reading your posts is that you're channeling all of your grief and anxiety into premature worry about college admissions... as if you can make everything right with the world by bringing a fantasy of getting into The Best College to fruition. The problem is that there's no college you can go to that will magically fix everything from the previous 18 years of life, so this way of managing your emotions is guaranteed to backfire later, whether it happens when the college decisions disappoint, or when the Dream College itself disappoints. (Because when you get there, you'll still be you and all the same baggage will still be with you.) I speak from experience on this; deal with the real issues now, so you don't have to spend college-and-beyond dealing with it when it catches up with you.
2 best idea is: imagine that you magically knew that you already had a guaranteed acceptance to a college you're thrilled about. Armed with that knowledge, what do you want to do this summer? Spend 80% of the time doing that, and 20% doing unfortunate practical things like test prep. (Maybe even 90:10) Seriously, what would recharge your batteries this summer? Getting away to some residential program/camp and making new friends and forgetting all about stuff at home for a while? Immersing yourself in something creative - art or music or theater? It sounds as if you're fortunate enough to have choices and aren't under financial pressure to get a job, so... invest in your health and well-being and growth as a unique human being by doing something healing and nourishing. Your current tunnel vision will tell you that this would be a compromise, but it really isn't, because anything that heals and nourishes you will also help you get in touch with the genuine passions that will come across in your college applications. Use this summer to get out of the trap of second-guessing what somebody else wants to see. No community college class on your transcript is better than the qualities and skills of self-knowledge, self-actualization, and self-care.