Well for minions kills we all started like that don't worry ^^
With training you'll get better, you should fix some aim in creep score.
For example I aim for 80 cs at 11 min, 125 at 15 and 200/250 for 25 depending which lane I play and how the game goes. Midlaners usually have more farm than the rest and usually have 10 creeps per minuts, often more if they also farm wraiths in jungle.
Well anyway LoL is a game where you will always improve, even pros are improving despites they are already pros.