Not to be a downer, but writing a book takes a lot more than just writing it.
It takes years sometimes. Writing it, re-writing, editing, everything.
I don't know you, but I'm saying you're not very old. So spelling mistakes will be all over the place.
Before you even consider sending it to a publisher, you and some close people (preferrably adults, yes, they may make fun of you, but they're more like to give you constructive critiscism than your friends are) to read it, and give tips.
I'm not going to mean, and say you've got a 0% chance at this. IF YOU REALLY WANT IT, I'm sure you can do it. But it's going to take lots of effort, time, and perhaps money.
Also, be prepared for being shot down my publishers. Full grown adults, who write beautiful work, have gone to university for years, etc, get turned down everyday.
So make sure you want this, and you will stick with it.