I NEED URGENT HELP TONIGHT, HEAD GIRL INTERVIEW TOMORROW!!?

I have a head girl interview tomorrow and I've prepared everything and I was feeling quite confident until i had a little look on the internet and everyone is saying that if you act like something you're not they they will rule you out immediately. There are 6 girls in for it and I'm not the favourite amongst my year group. I am a very outgoing and happy person and I'm from Scotland so i do often speak in slang. But i have written my speech and it's very formal and I'm scared it will sound like I'm trying too hard or I'm pretending I'm something I'm not? I'm just starting to worry about it because i really really want it! I was just wondering if the formal style of my speech will put me out of the running? Thank you for my help xxx