Christianity had no official name till the Catholic Church, founded by St. Peter (as commanded by Jesus), formed and became THE Christian church. Before that, there were multiple small, disorganized groups, not even aware of each other, some in hiding depending on their local Jesus, Sermon on the Plain:
Blessed are you who are poor, for yours is the kingdom of God. Blessed are the meek, for they will inherit the Earth. Blessed are the pure in heart, for they will see God. Blessed are the peacemakers, for they will be called the Sons of God. Love your enemies and turn the other cheek. Treat others the way you want to be treated. Don't judge and you won't be judged, don't condemn and you won't be condemned, forgive and you will be forgiven, give and you will receive. Remove the log from your own eye before attending to the splinter in your friend's. A good tree does not produce bad fruit and a bad tree cannot produce good fruit, each tree is known by its fruit.. The word "catholic," by the way, means "including a wide variety of things," per the Oxford Dictionary. The Catholic church gathered all the little sects together under one umbrella. It was THE church until Martin Luther's revolt in 1517.
How do you not know this about your own religion?