Life is Unfair

How would you feel if you've been given a grade 3 in a six units subject,  when you deserve a better grade?? It seriously pulled down my CGPA. I have good grounds to believe that my professor graded me unfairly, out of mistake. My classmates who have grades lower than me, got a grade of 2 :( I have nothing against my professor coz I know  humans are subject to error.  I appealed my grade to my professor, and she eventually realized her mistake. But she said the grades are already locked. She could no longer change mine. How sad. Moving on with a heavy heart :)