Ouch! Hope it's easy to sort. Unfortunately it's easy to be distracted.
I never fully trust hill hold. Like you, I have to park on a hill everyday at work, and it being DSG can't be left in gear, so I never release the foot brake until I've heard the reassuring crunch of the handbrake being fully applied.
Have had a near miss though, parked up facing downhill and unwittingly left the handbrake off all day to return to find the car headbutting the hedge which divides the next level of parking spaces. Thank god for that hedge otherwise I would've found my car at the bottom of the car park, no doubt in a sad state

I could park on the less steep lower section but then that puts you in with all the inconsiderate drivers who fling their doors open onto yours and I've had enough door dings inflicted on other cars to tolerate that any longer.