Plan B advice????

I had unprotected sex (pull out) 2-3 days ago. I think he came inside me a little. plan on getting Plan B, because I read that if I take them at the same time it can work...I'm too young to have kids. late teens, but I know I messed up. I made a promise to myself, to God, that from now on I will wait till marriage. I messed up. I know. just help, I'm desperate. and need somebody..