@NewLifeChristian, if you are unsure about whether God exists, you are an atheist unless you are illogical. If you don't know something, the default position is that you don't believe it. I don't know for sure that unicorns don't exist, but I don't actively believe that they exist.
@Texas14 That's not true. Someone who is unsure of God's existence is an agnostic. The definition of an atheist is, "one who believes that there is no deity." There is a difference between believing that something doesn't exist and being unsure of something's existence. If you are unsure of something's existence, then you are an agnostic.