What happened if you did confess to witchcraft?

That would depend largely on where the person was, who the person was and who the accuser was. There are some areas of the world where an accusation of witchcraft is a very serious matter and could easily result in the death of the person, regardless of the reliability of the accuser and any evidence. In other places there would have to be some evidence of the person practicing magic, but the accused would be punished or even killed. In yet other places, the accuser would be laughed at and not taken seriously at all, or at least no one would much care whether or not the person was a witch.

It really all depends on the local culture.