This is why I hate these kinds of relationships. Once you cross their line, there is no turning back. Too fine a line between BDSM and a domestic abuse relationship. She can now send your ass to prison since she decided your crossed the line. Better to just avoid these. However, if not, get documentation like texts that proves she has been asking to be punished that hard. Don’t feel guilty about this. She’s the one asking for it. You made a mistake you didn’t know about. If she set no limitations, she should apologize. Only she knows her pain tolerance. She needs to make you aware of that.