Should I tell my parents I'm not a Christian?

Tell them. You don't want to live your life like this. You don't want to decieve yourself or your parents. Religion controls too many factors these days and causes too many problems. You should be proud of yourself and stand up for what you believe in. Your happiness should come above everything else in regards to your parents. They may be angry at first but in the long run they will respect you for your individuality.