How can I convince my mum to let me see the movie? HELP!!! PLEAEAEASE!?

I'm 13 and my friends are going to see the Dark Knight, but my mum won't let me. I've read really dark and eerie books, like Tithe by Holly Black... my dad's seen the Dark Knight and he too doesn't want to let me, but if I can get my mum to say yes... well he doesn't do the parenting thing, he just goes along with what my mum says. Anyhow, how can I let my stupid over-protective-never-let-me-have-any-fu… mum let me see the movie? I really wannna see it, everyone says it's really good, and I have the money to see it, I've been saving up.