as a white person (which i'm assuming you are) it's common to emulate/repeat racial stereotypes. in brazil we had a case where a famous singer, while staying at a hotel, mistook another guest (who was a lawyer, if im not mistaken) for a cleaning lady. nothing indicated that she was one, she wasn't even wearing an uniform. but this singer saw that she was black and immediately assumed that she worked a low paid job. sadly, it's engraved on the minds of white people that people of color work minimum wage, and statistically, that is true, but it's still racist to assume that every single one of them does not have a successful career and that all of them are ready to serve you.

you were conditioned your whole life, unconsciously, to assume things of the sort. you can feel guilty, but use that as a motivation to learn more and be better. it takes learning, a lot of listening, and most times, experiences like the one you described. the fact that you recognized your mistake shows that you're on the right path.