Christians, if this is true, isn't our Religion kinda made up?

Thats an if. I've heard a lot about other religions that resemble christianity. They say horus was born of a virgin but there's no proof to show that The godess Isis was ever thought to be a virgin. She was infact a fertility Godess and a lot of lies are made up about these pagan religions to compare them but there could be some truth somewhere in it. I never heard of Osiris being born of a virigin though. Are you sure? I thought he was the god of the underworld.