If you use the Image Specs Tool and enter the URL of your image submission, you can see the amount of colours in your submission and how often each one is used. Your submission has over 400 colours and it seems like hundreds of them are single pixels, extremely similar to one another in value, all dotted around the picture. There is no hard and fast rule on the maximum amount of colours allowed for each submission (since the canvas size of the submission plays a factor into what's considered sensible) but this one doesn't seem very optimal or cohesive in its current state. 

 

A lot of people start with high-definition paintings or sketches and then scale them down to a pixelart-friendly size before cleaning them up; the important part is that you have control over the placement of single pixels and clumps of colours, rather than leaving it wholly up to the computer. There are lots of errant single pixels and clusters of colour here that would have made more sense with a higher resolution of detail to work, with on a higher-resolution canvas, but that detail was lost in the scale compression. If you don't put the work in to display a control over pixels, then a careless impression is what is left over.

 

I would ask that you find a way to compress the palette under 100 colours, give some sense into cleaning up the pre-existing clusters of colours, and then edit the page to submit that new version in the place of this one.