I hope you will be honest with your parents instead of trying to deceive them. After all, they love you and are concerned about you, and if they truly care about your spiritual welfare they need to know how to pray for you.
But more than that, I hope you will be honest with yourself. What has caused you to doubt your former beliefs? Have you been wrestling with questions about God you've never faced before? Or is it something far simpler: You are away from home for the first time so it's easy to turn your back on things you once believed? Or have you gotten involved in something you know you couldn't do if you had a strong belief in God?
Whatever the reason, I hope you'll face your doubts honestly and not simply go along with the crowd. After all, one reason you may be questioning your beliefs is because they weren't very strong to begin with. But God is real, and now is the time to discover not only that He exists, but that He loves you and has a plan for your life.
Jesus said, "Seek and you will find; knock and the door will be opened to you" (Matthew 7:7). Ask God to show Himself to you, and take time each day to study the Bible (especially the Gospels, which tell us about Jesus). Then seek out Christians on your campus who can answer your questions and point you to Christ.