How can I become more confident in interviews?

I am a final year law student and have gotten to interview stages at US/MC firms but have never passed. I feel like I do tackle the main points in case studies but I get so nervous and feel so much pressure that I cannot express these points clearly and concisely. When it comes to competency interviews, i just stutter and shut down when I face an unexpected question. Over time, and after each rejection, I seem to get worse at interviews because each rejection makes me feel like I do not belong. I do not know how to become more confident. I am extremely introverted and have Autism but even when I try put on my extroverted persona, I feel like it doesn’t come across as genuine (because it isn’t)