Why do catholics pray to Mary and treat her as though she is a God?

I have always wondered this, I grew up Lutheran and know the bible quite well. Besides being chosen to be the mother of Jesus, Mary is not holy in any other way. Why do catholics worship and pray to her like she is a God listening to prayers in church and have so many things dedicated to her in their services? Didn't God say do not have any other Gods before me? So why do catholics worship Mary?