I got a parking ticket and someone/ thing removed it! HELP?

I went out to lunch during school with my friends and was in a rush to get back. I found out later in the day i parked in the "motorcycle parking only" spot (yes ik dumb) which is rite next to where i parked b4 lunch (mistook that spot for the one next to it) I was in school when one of my buds told me i was being written up. i went to the door to look and i saw a ticket under the wiper. But i couldnt leave the school 2 grab it. i also had to get to class. I came back out when school let out and it was gone. Im almost positive someone took it as a joke because the wipers have a lot of force to keep the ticket from flying in the wind. I have no proof of being ticketed but the police probably took down the plate so im in the system. What should i do? and this is not an excuse to get out of 20 bucks because i wouldve payed the 20 bucks instead of trying to fight it. thanks