Got everything scanned and into the rucksack, collected Sophia, got to the top of the steps, opened my phone, noticed the lack of a "You just paid a small fortune to Marks and Spencers" notification, equivocated for about 5 seconds, walked back down, found a person standing near that till, discovered that when they cancel an order they get a receipt, took that to a customer service point, waited while they failed to scan it because the printer ink was running out, stressed about missing my bus (while being aware that it was all my fault), breathed a sigh of relief when eventually they guessed the missing digit, paid, headed back off to get the bus, made it with three minutes to spare.