Looking at the match, you bought 0 Control Wards, dropped 6 wards in 21 minutes 33 seconds, and denied 0 wards as well. You also didn't upgrade your FREE trinket upgrade at level 9, and had 41% kill participation with only 4 CS/minute. Try to aim for 6-10 CS/minute in the jungle, depending if you are gank/farm heavy. While it's nice consistently ganking for your laners, it doesn't help if you sit in a brush for 15 minutes without farming. Your damage is also extremely low for someone that was "ganking every lane so hard."
If you're aiming for S grades, you'll need to step up both your CS'ing and Warding game, as well as increasing your damage and Kill Participation. Zac brings a lot of up-front damage so there's no excuse for having such a small amount if you're ganking as much as you'd like to think (unless you're missing every single ability - which is a different problem on its own). When you have an item like Sunfire Cape and an AoE on your W/R, you should easily be obtaining a higher KP (Kill Participation) if you're ganking frequently, as you "tag" a lot of players just from existing around them. For reference, at 10 minutes a higher MMR jungler will have the same CS as you did in 20. The changes to Krugs and Raptors make it so you can easily get a significantly higher Creep Score than before, even when ganking. You get 10 CS for Krugs, 6 CS for Raptors, 1 CS for Red, 1 CS for Blue, 1 CS for Gromp, and 3 CS for wolves. That is 22 CS for just clearing your own jungle without taking any enemy camps, Scuttlecrabs, laner farm, or Dragon/Baron/Rift Herald. 4 Clears would have netted you 88 CS in under 7 minutes, as they are on a 100 second respawn timer (1:40).