Since when has ignorance ever been an excuse?

You think a cop will give a flying fuck if you "didn't know" that the road you thought was 65mph was actually 45mph?

Same goes here.

You are supposed to use sensible judgment. That said, I'm sure based on what kind of luck you have with the judge, prosecutor, girl's parents, etc, nothing might happen but you can rest assured that ignorance alone will not be your saving grace.