I've had a similar situation, but it wasn't a 'first timer' mistake ...!
I'd booked to go see someone in London, and when I get the postcode details the best option was to go there on the underground. Actually, I was always going to go on the underground, but the punt location made me choose one particular line over another. Drive to the station, found a street somewhere to park nearby, and walked to the station. I start searching for my Oyster card which is in my wallet, when I discover I've forgotten to bring my wallet with me!
Back to the car, and drive back home again. Get caught in bad traffic, I decide to call the SP to let her know I will be late, or to cancel; just as I dial the number my phone-battery goes flat!
When I eventually get home I give the phone a quick charge, phone the SP and tell her I'm stuck on the M4 traffic and will have to cancel. She understands and is quite okay with it.
I never did get to see her
(so please don't badger me for a review!)