HELP HELP HELP!! Teenagers making speeches in competitiions

Hi, i am still in school. Within my school they divide the student body into four houses (Bit like Hogwarts) I am going for the team captin of my house in year eleven. I am reqired to speak infront of 450 students (my house) and earn the students votes in 2 minutes. I have two people running against me who are very popular and brainy. I am very brainy and relativly popular especially with the teachers. But these two students are everything. I'm so nervous, i dont think i stand a chance, help me out - i want this role SO BAD, but i fear i'm going to drop out.