You don't stop being a writer after you finish writing that book. Like I said, during your time away from writing, try to consume more media. Becoming overloaded media is a thing though, so don't go overboard with that either. Like all things, do it in moderation. Writing a story is tiring and all-consuming that sometimes your whole world starts to revolve around it, so when you finish, celebrate a little and put it away. Morbidly, I like to joke that I'm free now; I did my work diligently, and the story, my master, has given me, Dobby, a sock. Dobby is a free elf!
If you're feeling confident enough, and I think you should be, try posting it online or sharing it with friends. Wattpad is a great platform for that, but so is Tumblr or your own blog. If you're interested in getting published, write a query letter to an agent or a publishing house or try submitting to Swoon Reads. I don't know enough about the publishing industry to help you there, but research is your friend. So is Google.
Be proud of yourself. You made something out of nothing and stuck to it long enough to finish it. Not everyone can say that about themselves.
If you had fun, try it again, this time with a whole new idea. If not, then at least you tried. Life generously rewards those who go out there and try. If you're a believer like me, then know that God, Our Creator, who made us in His own image, would be happy to know you have made good use of His gifts, and if you offer it up to Him, He will make it a blessing to everyone else. If you're not a believer, then the same thing can be said about this beautiful, wonderful universe that seemed to appear out of nowhere.
Your story's a little universe, too, and you should be proud of that.