Step 3: Scale your image
Time for the conclusion.
In the Image menu, choose Image Size (Alt+Ctrl+I), set the Resolution to half of what it is now and press OK.
See second attached screenshot.
Voila! Photoshop has added anti aliasing, a sort of precise and systematic blur, to the edges of your drawing and you're left with a neat and crisp image that you can now add colour to, or whatever you want.