Your situation is soooo familiar to me! I was brought up catholic, but I never was able to buy what they were trying to sell. It just didn't make sense to me at all. I kept quiet, and I was a deeply introspective child. I didn't want to disappoint my parents or friends and family. But you just can't make yourself believe something that your logic is screaming at you is wrong. I, to this day, cannot fully disclose to some of my childhood friends my views on religion and god. It's just kind of a don't ask and don't tell type thing, but still their beliefs sometimes make it uncomfortable for me to be around them a lot. I do know this, the moment I came to the realization I was atheist, or rather the moment I admitted it to myself, I felt free. It's like finally allowing yourself to be free. You are young, and you have the rest of your life to use that freedom to ask any and all questions that you need answered without fear or internal struggle. You will meet people who are like minded, and exchange ideas, and find out that you are going to be just fine!
Now you get to get on with the rest of your life, limited only by yourself. You can ask the big questions, and seek out, guilt free, your own answers. They will be so much more satisfying, because they are YOURS. You are now outside of the sheep pen, and free to roam wherever your heart and curiosity takes you. Simply be who you are. If people can't accept you, for who you are, then they probably aren't good for your life. Not going to say it's always easy to think the way we do, but being truthful to yourself, seldom steers you wrong! Congratulations on your great revelation. I'm not applauding that you don't believe in god, I'm applauding that you had the courage to ask questions and come to YOUR OWN CONCLUSION. These are the kinds of people I admire! :)