I don't know about your school. At ours, the grades are unofficial when first posted. That gives the opportunity for students to go over their grades and check if there are any mathematical errors. It does happen. I know of at least two people who had grades adjusted up for math errors.

I don't know if a professor would check the math if you got an A, and adjust it down, but why take the chance? The bad grade, go over now. The good one can wait.