It would help if you posted the piece, so others could see it.
I found it though:


It doesn't appear that you credited your reference. Always credit your reference! Even if you don't know who the original artist was, or even if it's a well-known image, always be clear that you used a reference and link to it if possible.
In addition, it looks like you traced the reference, your pixel art matches the ref almost exactly. That isn't necessarily grounds for rejection, but you have to be clear up front when you trace! Tracing other people's work is generally frowned-upon. Tracing your own work is fine, and tracing is often accepted when it's only a small part of the artwork and the final result deviated from the original significantly.

You also seem to be mixing pixel scales. Some of the "pixels" are 2x2, some are 1x1. Don't do that unless you have a very good reason to. Better yet, upload your work at 1x zoom, so all pixels are 1 actual pixel.

Lastly, the actual pixel work feels a bit noisy and unfinished. There are numerous stray pixels and some jagged lines.