Free Traffic Legal Advice

I have parked on the street to take my son for an appointment. He is disabled, and the Blue Badge is in his name. I forgot to put out the badge and when I returned to do it few minutes later, I already had the notice on the vehicle. The parking attendant was still there so I told him I forgot to display the Blue Badge and what should I do. He said to appeal and they will cancel it. But reading other fora I see that there seem to be not much I can do. I put it here for advice if it is worth appealing. The PCN and the signage pics are here: ,
Thank you, Chris.