I made a mistake in a test but got 100%?

Hi all

I know this may be awkward, but I am an honest person, so I've been wondering about this.

I'm in my final year doing Economics and I got back a quiz test we had the other day (it only counts with 4% towards the overall grade, so it's no big deal). I did everything correct except for the last question, but I got it ticked (as if it was fine) and got my 20 points (out of 20).

I feel like I don't deserve 100% with a mistake (there were 4 questions and I got half of the last one wrong) but don't want to 'lecture' and 'correct' my tutor (I know teachers hate when students are playing too smart). But on the other hand, he may as well appreciate my honesty (or think I am a total idiot).

What would you do in this situation? Are there any 'rules' about this? (it's a good uni in Scotland) Am I kind of legally obliged to report it, or once marked, case closed?

Thanks