How did i not get an S

So i've been 1 game away from mastery 7 on pyke for little bit now, but i finally had the game where i thought i would get an S at least. I when 4/1/13 in 20 min game, got FT, 47 vision score, my CS was 6 (i took coin) we got every drag that game. it last 20 mins so i really want to know what i could have done to gotten an S atleast (edit: i like to make a small point that i had gotten about 7 asset be for i hadd ult and only had one non ult kill)