Theo is in a large lecture history class. The professor for the class gives a weekly 10 point multiple choice quiz. The professor always reviews the correct answers after returning the graded exams and tells students to let him know if there were grading errors. Theo had caught a grading error three weeks ago where a problem was mistakenly marked incorrect. He showed the professor and immediately got his grade adjusted from 8 points to 9 points. When the exams are returned this week, Theo is delighted with a perfect score of 10, but his pleasure is short-lived for as the instructor reviews the exams, Theo notices another error, but this time the error is in his favor. He actually got a question wrong but the instructor didn't mark it down.
It's a matter of honesty. Sure it would have been great to have a perfect grade on the exam, but if you missed the question, then it isn't really a perfect grade and it wouldn't be fair to yourself or to the rest of the class to have it counted as such.
And there are plenty of professors out there who would give you at least partial credit for your honesty and integrity.
Or, even better, a good letter of recommendation.
You don't deserve the points because you didn't get the question right. It's a question of fairness and honesty.
Why bother. If the professor didn't notice, it's not your job to do his job.