Im no pro but how is that not an s

I played the most insane game as fizz I will ever play. I know I'm going to hell for playing him but I don't know how I didn't get an S. I know you need perfect farm but for assassins, you shouldn't have the limit so high since you farm champions. I will never get a game like that again. You could atleast give me an A+ or an S- at best.