Whenever I return an exam to my students, I tell them the first thing they should do is to add up all the numbers in the left margin, one by each question, to see if they total the number in the circle at the top of the front page. If they add up to more than what's in the circle, I ask them to tell me so I can fix the mistake. If they add up to less than what's in the circle, I tell them that I'll correct the error if they want me to, but I don't expect them to say anything.

Same thing with airline miles. They'll probably fix it if you ask them to - though it's not unheard of to get a "keep them as a reward for your honesty" letter - but they won't hold it against you if you sit down and shut up. Don't let it bother you. How long would you fret over a dollar bill you found in the middle of an empty parking lot?