If you just keep "Sketching" you are teaching yourself to make the same mistakes over and over again.
People think drawing is something you learn to just do where it just flows out of you and you don't make mistakes but that's bullshit. It's very, very, rare to find someone who can just sit down and draw a perfect image.
Drawing, and in many ways all art, is about fucking up over and over and over but learning to see your fuck ups and correct them.
You can't be afraid to fail. Art is always 80% failure!
Building on top of and refining failure is how you get stuff done.