So you hand-picked all 253 colors? If that's true, you're still not having much control over the piece, as there as several hues that indifferential from one another, making the majority of them extremely redundant. And also, the "brush" tool in Photoshop usually auto aa's, and tends to blend colors together, adding unneeded color count to your piece. I'm sure after a bit of time, however, you'll get the hang of it, as we all have issues grasping pixel art in it's beginnings...

 Really? I did each pixel (apart from some of the body where I used paint brush to get filled colour) one by one.

Good Gawd, 253 colors! This is definitely not pixel art...Looks like a lot "brush" tool was used here, as well as Auto AA function...I guess if you're a beginner to pixel art, you're bound to make mistakes such as these. Just remember the key to pixel art is control; you must have control of detail on the pixel level...auto tools tend to lose this control, and things tend to get out of hand, in terms of quality...in any case, sending back for revision....keep trying though, I'm sure you'll get the hang of it!