That One Moment with the Customer

I'll never forget the day I overcharged a customer by $20. It was such a small mistake, but it felt like the earth had moved beneath my feet as soon as I realized. The customer was so nice about it and patiently waited while I double-checked everything to make sure they got the right change back. But ever since then, every time someone pays for their items or asks if there's any kind of discount, I feel this knot in my stomach tighten. I worry constantly that I'll slip up again somehow, even though logic tells me it was just a one-time thing and I'm being overly cautious. It's like the incident has branded itself into my memory as some sort of cautionary tale, replaying over and over again every time I work a shift.