Something exactly right is precisely, totally, completely right. This is a word with no fuzziness or wiggle room.
Isn't it nice when you know exactly the right word for something? Well, exactly is a word for when you're talking about things that fit perfectly or are unquestionably correct. Ten plus ten is exactly twenty. There are exactly fifty states. An astronomer could tell you exactly how far away the moon is. Exactly is the opposite of approximately or roughly. If you don't know for sure what you're talking about, don't use the word exactly.