Missing Champion Mastery Points

was on the free champion rotation for a week, I used her since I have a free skin for her. I managed to reach Champion Mastery 2 on her when I used her for free. But now after I bought her, I realized that the total Champion Mastery Point doesn't add up. I have 148 now, but after I bought her, I should've gotten 150, but it didn't. Is there a bug or something? or do I need to level her up to level 3 Champion Mastery Point?