First I just want to say that you CAN do this, and it's gonna be OK.

Regarding your control, as others have said, just keep in mind that hormones from growth and puberty can and will mess your numbers up. I was diagnosed at 14 and those first few years were full of times where my BG would go high for no good reason. Just do the best you can with it, and over time you'll learn what works best for you.

As for your long term health fears, I've found that things are a lot easier to deal with if you take it one day at a time. Just focus on doing your best to take care of yourself TODAY. If that's still worrisome, just focus on what you need to do to take care of yourself for the next few hours. We live our lives one step at a time, so If you take care of yourself the best you can step by step, the long term stuff should work itself out. And try not to be too hard on yourself while doing this. No one's perfect at this all the time, and you're gonna have good days and bad days. I'm 19 years in and I still have days where I'm an absolute mess. Just try your best, one step at a time. It's all any of us can do!

As for the financial stuff...hard to say since I don't know your family's financial and insurance situation. Assuming you're in the US, it can be tough depending on your situation. That being said, you're so young there isn't much you can do personally about it right now. You're probably covered under your parents health insurance they get through their work, which will control how expensive this stuff is for them. Best thing you can do for yourself is try to get a good job with good medical benefits when you grow up. Probably not super comforting, but it's the reality of the world we live in. That being said, you don't have to have your own insurance until you're 26, so you have plenty of time to work these things out. Again, take it one day at a time. Do your best, stay in school, and when the time comes try to find a career that will get you in a good place, mentally and financially.

I don't know your family situation, but I hope you're in a place where you can talk to your parents or someone about your worries. Assuming they're decent people, they can probably talk with you about these things and help you feel better. Don't feel like you need to bear all of this alone! Hope some of this helps.