I do go by the official grade'; it's just a bit annoying.
As I understand it, the only reason you should be retaking a test is if you fail. And then the highest grade you can get is a 60. So I think that's the reason your grade wasn't changed.
My issue is that the grade was wrong the first time. I got 17 out of 20 correct, meaning 85%; but it was graded as 75.