Getting sharp edges is something even the $100.000,- scanners still have trouble with, that's why there is some very expensive post processing software available to get the scan to it's original sharpness and shape.
you still have to do a lot of manual work.

The only way you can get sharper edges is scanning large size and shrinking to a smaller size.

You could also try Blender, I've seen some tutorials on how to sharpen edges with meshes, but you would need to redraw a lot.
https://www.youtube.com/watch?v=IKABoq5sIEM