I genuinely think that my life is over. 17M and I'm turning 18 in a few weeks, but my life is in utter shambles that I don't think I'm ready for the real world just yet. I have no hobbies, and I don't think I can even enjoy new ones right now because I have to get ready for college. I've fantasized times where I could just work part time so I can do something productive instead of consistently failing in school, but I'm so scared of what my family or relatives might think of me when I do. I consider myself as a people pleaser, but I couldn't name someone I actually pleased with my presence. I've been like this for 3 years, but 7 months ago a great woman changed my life for the better. That was nice, until I messed up and got too overemotional and said things I shouldn't have. It's been a week since she last texted, and I know for sure that my life is only down from here. I'm scared, I think my life is over.

I've been in this exact same situation before, and honestly the best thing to do is to keep going on with life.
Live in the moment and see where life takes you, you never know what's in store for you.
Things will get better, and worse, and better again, because life is a rollercoaster of emotions and will always go up and down and take you through loops and twists and turns.
Of course, don't just forget about your future or your past, keep them with you and plan for them, but don't be too focused on them, because in the end they'll just weigh you down.
This is all coming from my own personal experience, of course you are your own person and things will probably be different for you, but I hope this helps, or at least gives you some peace.

It's understandable that you're feeling this way. You are at a point in your life where you're going to be facing a lot of pressure over large decisions people around you and society at large says you need to make immediately. Understand that you have time though and with all the years ahead of you there's so many big changes that can happen.

It sounds to me like you have a lack of direction and/or purpose right now. Your fantasies of just being a little productive instead of consistently failing school might not be so much a fantasy and just genuinely what you desire. You might be well served by putting college off for now and just try working a bit. With your free time you can consider taking some random workshops for things you might be interested in or that are just useful like CPR/AED certification classes; such things can provide an opportunity to meet people and at the very least will give you some good things to put on your resumes/applications for jobs. After the year ask yourself for what purpose do you want to go to college. Is it for some specific path that requires college or are you simply going to college just to go to college? If it's the later then I highly encourage you to consider something else whether that be trade schools, getting certifications rather than a degree or just pursuing jobs that don't require degrees. Going into college without a clear goal is more likely to just put you in debt and leave you feeling even more overwhelmed.

As for the girl who hasn't messaged you back, it's hard to give advice without specifics, but I can say that if you feel bad over what you said then all you can do is apologize and proceed forward with your life. Hopefully she'll message you back and at least give you a chance to discuss it further, but if she doesn't then you have to accept the consequences and endeavor to have better control of your emotions. The memories might be bittersweet if she doesn't contact you back, but it shows that you can have sudden improvements in your life by meeting just a single person.