Then I wouldn’t. There is no requirement to self-report AP scores. You aren’t lying. They will only consider what you give them, not what you don’t give them. It’s up to you of course, but a three will not be impressive. Would you tell them you got a 75 on a test, even though you still got an A in a class? If a college gives credit or placement for a three, you can always submit officially before matriculating. For the schools you are looking at, do not submit a three.