Fizz and those watery graves

So I've been playing league for about a year and a half and I'm starting to take a liking to one of my favorite champs again, fizz. Ok so the problem I'm having is my creep score every other champ I play I'm at nearly 150 at 20 and 200 by 27-30 not the best but it gets me there. Fizz isn't the problem I mean I look back at my history and every game results in me getting fed to shit and I can 2 shot carries. So the question I have is should I even be worrying about my cs as fizz or what can I do to improve. Also the harass from other champs doesn't make it any easier.