Look at the science. Life begins at conception. It is unscientific to say otherwise. All you need do is look at a picture to know an unborn child is not just a "clump of cells" or a "potential" human being An unborn baby is an actual human being and abortion is murder.
Why are you almost certain? It doesn't really make sense to think that He doesn't exist.
I know that God exists. All you have to do is look at the design of the universe to know that there HAD to be a creator.