1. An A- is not a "harsh" grade.
2. Indicating that you've read my "opinion" about your grade but do not agree with it--in other words, challenging a grade by implying that your opinion and my professional judgment have equal weight--does not require me to change the grade, even if you have rendered this disagreement in respectful, if overly familiar (HEY UNDINE) terms.
The great lesson of adulthood is that you don't have to like everything you do. You just have to do it.