Parking Tickets: High School Parking Ticket

My question involves a traffic citation from the state of: Iowa

I received a parking ticket in a high school parking lot for failing to display my parking permit. The permit was displayed like it always is from my car mirror as it is supposed to be displayed by the rules in the school handbook. It was clearly visible and I was parked in the correct parking lot, etc.

The school principal will not consider that this was given to me by mistake. What recourse do I have?

Parking Tickets: High School Parking Ticket