Social anxiety and medical interview next week

I recently graduated from high school and have a medical interview in under a week. At this moment I think there is almost a zero chance of succeeding. Although I haven't been officially diagnosed as having social anxiety disorder, I believe that I've had it, or at least some other social disorder, since I was young. I used to always become mute around other people and until this day, I speak extremely softly to the point where so many people repeatedly ask me what I said or nod at the wrong times. I also feel so self-conscious and I hardly smile or laugh (I mainly smile close-mouthed which doesn't look very happy and don't even laugh that much with my friends. I have a very bony face, huge teeth and braces too so when I open my mouth I think I look monstrous, so that makes me more self-conscious). In social situations, especially involving large groups of people or just certain people who I feel more nervous around, I feel so nauseous and this year especially I've avoided them using study as an excuse. I struggle with thinking on the spot in front of other people. When I did two mock interviews, I didn't improve at all; I could hardly form coherent sentences, struggled especially to think while maintaining eye contact, resorted to closed body language and struggled to smile.

I am almost certain that 1 week is not enough for me to fix all these problems, however I was wondering whether anyone has had experience with this and/or could provide advice for me to improve. I've volunteered at several annual events for around 4 years and currently work in retail but I don't feel like this has helped either. I can smile and say "hi" and "have a good day" but I don't really carry conversations with my customers because I don't know what to say.

I don't want to write too much but I honestly do have such a great passion for human anatomy and pathology, something that has fascinated me from when I was eight years old. Although I don't fare well in social situations, I really do want to help people, often going out of my way, but I just automatically mask myself and my mind doesn't work properly.

I am sure that you are questioning my suitability to gain entrance into medicine, and I am too. However, I've decided that I'll still try my best and that I'll have to improve on these skills regardless of whether or not I succeed in interviews.

Thank you.