WOW I am really sorry that these young 'Christians' have insulted you. I hope that as they grow up and grow in their learning about Christ, they will realize that it isn't the PERSON to be "hated" but 'sin' that God hates.
Being an atheist just means you haven't found (a) God yet. Until something comes to you that fits that category, you have every right to say you don't believe, that's just the truth!
Please don't judge all Christians by these classmates. If you give some examples of what they say to you, we can help you help them understand the real relationship they need to have with all people.
TC