Do citizens have any protection against unknown laws?

I received a citation for cl B misdemeanor while babysitting my nephew because I was not aware of laws about leaving a child unattended for more than 10 min. The child was safe, I would not have done it if I had known it was against the law. Do I have any protection? The Judge said I won't go to jail, but I plead not guilty because I really can't have that on my record. I meet with the prosecutor in a month. Any tips? I have never had trouble with the law before.