Well, it doesn't look like it was made "pixel by pixel" or more accurately, with a "
pixel precision". It looks like more like a "classic" drawing (I mean, with mouse or pen, but with no intent to place pixels to form a specific shape), mixed resolution and use of symmetry doesn't help too. I'll pass on lack of shading as it is obvious there are bigger problems.
You should try simpler shape, and learn some basics about drawing
