Hi, ej,
Thanks for posting. There's not much I can do for you -- writing is a solitary profession, done alone, for the most part. I can only advise you to make an outline of your entire story, chapter by chapter, writing down what each chapter will contain, how much of the story will be contained in that chapter, and who the narrator will be. Planning is everything when you're writing. That outline will be what you can work from.
Good luck! -----Gordon Korman-----
... and P.S. I was 12 when I wrote my first book, so there's no such thing as being too young! Again, good luck!