Why would you even bother sitting and calculating someone else's marks, to prove they should have been awarded a worse grade? Just focus on your own grade, it's great, well done you. But to try and devalue somebody else's achievements isn't cool IMO.
It's probably just one of the first of many times that you will find that life isn't actually fair.
EDIT: Also, our uni put more weight on certain modules, like the dissertation and the written exams, and less weight on assignments through the year. In addition, our third year was worth more than second, and first didn't count at all. Are you sure you know how much each module is even worth?