Is Christianity monotheistic?

We Christians only worship God. God is a trinity, 3 in one. The simplest explanation for God being a Trinity is like I am 3 in one. I am a poet, disabled, and a group owner. All are me, and I am all. I can't be in 3 beings, but God can. People are made in God's image, so we are multi-taskers also but God is the only God. Mary is a human woman who bore Jesus here, nothing more, saints are people who did wonderful things, and are recognized to be God's instruments, angels are God's servants. Jesus is God's Son, who lived here on earth.