Im nervous for musical tryouts and im not the best....any tips?

My school is having a musical called Thoroughly Modern Millie Jr. and i wanna be Mrs. Meers cuz she is a comedic villain. I'm quite funny and lots of people think i'd get the part, but im not much of an actress or singer......i also can get a bit scared and forget things when im in front of a crowd. Even my homeroom. Any tips?