OK, this might not help yet, but what I will say is that you don't have to suddenly overcome this all at once. And even if you do go to university, it's not the case that you will suddenly be expected to do lots of presentations.
I have severe social anxiety too. Fortunately I never had to do any during college, but during my undergraduate degree, the two presentations I was supposed to do I was given mitigating circumstances for, so that they were not included. In fact, my student adviser's advice was to not do it even if I got a mark of 0, because one grade is such a small part of the overall degree.
Then, when it came to my Masters degree, I had to start speak - there were only 7 of us on the course and I was absolutely paralysed by fear. So my supervisor built up very very slowly with me. Painfully slowly. We started where he would e-mail me some questions and I would e-mail my replies back. Then he started to feed those back into sessions and say them for me, so that I could learn that my contributions were ok without being judged or having to use my voice. Then we built up so that he would ask me a question that he knew I could answer, and I could give a one word reply back. And eventually it built up where he asked me, and I managed to whisper a whole sentence aloud. If I couldn't cope, I could just write it down or whisper it to the coursemate who sat next to me, who would say it for me instead.
That's a bit rambling, but I just mean, there are people who will understand, and they can help you work on this (if you do decide to go to uni). And things can improve. I still have absolute terror and severe social anxiety, but I managed to get on a plane alone, fly to Scotland (from Sussex) and conduct focus groups with senior Civil Servants last year. So it is possible, I promise!
For now, I'm guessing that your tutors are aware of the issues you have? Can you let them know (either in person or in writing) how much you're struggling with this and how much it's impacting your health? I know it seems such a massive deal at the moment, but ultimately, it is not worth making yourself so distressed over, and if you're not up to it yet, that is ok. It doesn't mean it will never get better.
How are you doing now?