Hey @OMAMfan,
Thank you so much for being here and sharing some updates. Summer and end of school can be such a relief! But then you realize: eh, but I’ll have to go back there soon, and the stress will just come back up… As a pretty anxious person myself, I can tell that years of school felt like a constant rollercoaster, and just knowing when school will start again was quite stressful in itself. It feels like starting over and having to learn to be familiar with the place again, yet with the same people, and the same issues that were on hold for a couple of month. How you feel makes sense, friend. And it’s really good that you’ve decided to take some time to write it down and talk about it.
When we feel stuck in our worries, overwhelmed or burned out, just acknowledging what’s going on in our mind and what stresses us is a huge step in itself. Of course, it’s not a magic wand and it doesn’t solve everything instantly. But it’s still a right thing to do, because as you described very well: trying to hide your fears, ignore them or put them under the rug just makes them bigger and even more frightening. The more you face your fears, the more you learn to be familiar with them, and less they seem overwhelming or impossible to overcome. So, well done for being here and reflecting on your own anxiety right now.
I’m mad at myself for getting involved with people who were not good for me. I have my issues I try to fix but I had to cut these people out of my life for the way they were treating others.
I understand why you are mad at yourself. However, I’d like to encourage you to give yourself some grace and credit there. You are not in this situation anymore… and even more: you actually made some tough decisions in order to get out of a situation that was affecting you negatively. That’s actually VERY strong! It’s something you can absolutely be proud of. Because you could have decided to stay, but you didn’t. That itself displays a lot of bravery on your end. Sure, it’s frustrating to review your past and think that maybe you should have make different decisions earlier, or not even allow yourself to hang out with those people. But that’s also just part of life - we can’t always guess who people are at first. Yet you have learned and grown through this situation.
I know it may be irrational because I have no clue. It’s just nerve wracking thinking about school starting back in a month seeing them for the first time since I cut them off.
Yes, that makes sense. All the “what if” questions that our anxious mind can start to ask once we are lost in our thoughts. It’s an endless pit of stress if we are not careful of how far it brings us sometimes. So it’s important to remind yourself that at this point these thoughts are only thoughts. Nothing happening right now. Another thing you could ask yourself is: how can you anticipate, eventually, this situation from happening? What would be your options? Having a plan of action, even if only hypothetical, could help to ease your fears as well and regain a sense of control over something that worries you.
However, that only gets me so far. I start to obsess over college life and fantasize on what could happen. I think about what could happen if I can’t afford it or I screw it up somehow. I then get mad at the simplest things like getting asked to do something or I just lie in my bed drowning in fear and confusion.
That’s the terrible curse of anxiety. As much as it’s important to think about our future and learn lessons from our past, it’s also as much important to try to ground ourselves in the present. Anxious thinkers like you and I spend the most of our life inside of our minds, forgetting all that is happening around us in the present moment. It’s a learning practice, but I personally believe that the more we try to ground oursleves in the present on a daily basis - even as a start, just 5 minutes here and there -, is already an incredible help in the long run. Takes a bit of time and discipline to see its effects though! But it helps to set some limits for when our mind wanders too deeply. Again, it’s good to have plans for the future, but when our anxiety settles, it’s generally because we only focus on the goals to achieve, and we forget all the intermediate steps in between to get there. Basically, we don’t learn to walk on a staircase from the first step directly to the last one. We do it step by step progressively, which makes our goals more achievable, realistic, and safe.
I’d highly encourage you to try to develop a journaling routine as well. Try to use some time on a regular basis to intentionally write down your fears, even the most unrealistic ones. Just writing down things out of your mind and seeing it physically could help you to reflect on those and learn to rationalize more and more the situations you’re in.
If you’d like to share your fears about your senior year and high school years right here, feel free to do so as well. Maybe conversations here could help you to replace those fears by something more realistic, and reassuring, especially since we have people of different ages here who have already been through what comes after school as well.
You are not alone, friend. I hope you can find some comfort and reassurance in this truth as well. Hold fast. 
PS - My apologies if I missed some words or mistyped here and there. Kinda struggling with a brain fog, but trying my best! 