I also have a speech tomorrow in front of 100 students in an auditorium and we have to give it as a part of practials in English subject holding around 40% weight age,and you may say leave it and score 35 out of 60 to pass,but the question paper is pretty hard, so one must give the speech. I have been feeling the same feelings as you and all I can think is about tomorrow. The only thing I'm doing from the past 3 days in reciting the speech in front of mirror.Also find videos on youtube titled as "practice speech infront of people" and play it on the largest screen you have.It does feel natural and record yourself speaking.Do it as many times you can