"Parking fees"

I had an appointment at 11:05 and left 15 mins later but managed to get a parking ticket for £90. I approached the ticket dispenser and saw "free for first 3 hrs" and not thinking didn't continue to take a ticket - not malicious or wanting to cheat the fee which was free anyway but more an oversight. Upon returning to my car after a blood test I had a ticket timed as 11:10, the parking inspectors must be hiding behind trees or concealed in bushes , maybe Ex special forces? Whilst I agree that a public service NHS hospital should be free the fact you didn't take a ticket is got a fine is concerning, as they say signs should be posted or even have an exit barrier that you need a token for -available from receptionist upon proof of appointment