First of all, I apologise. This is a really silly AIBU. So silly and such a non-issue that I didn't know what title to give it 
Basically I rely on my bank card way too much, and normally pay with it instead of using cash, as I find it more convenient.
Until of course the time comes when you buy something so small that it's not worth the shop's while to accept card payments. And you come a cropper.
I bought some bread this morning, and when they said they didn't accept card payments for it as it was so small, I found that I didn't have enough change to pay for it. By this time, there were a couple of people waiting behind me. I asked if I could pay with a £10 note I had, but the guy behind the till suggested that it would be too much bother. So I paid him with the change I had, and he told me just to 'drop round' the rest of the money I owed (50p...) when I was next in the shop.
Today is the first time I've visited the shop, and it's slightly out of my way. My AIBU is should I just not pay back the owed money, or should I go back soon to buy something else and pay the owed money? I do want to pay it back, but worried they'll think I'm bonkers for getting so hung up on it!!! Aaargh. I know I'm definitely 100% overthinking this....!!
Please help, Mumsnet, with this ridiculous AIBU!!