First of all, your picture isn't considered pixel art just because you used some brushes/filters and have so many colors. Typically in pixel art each color is hand-picked. But, that's no big deal. Easy to fix; just draw over it with a pencil tool or opaque brush tool with no auto-aa.
*edited to change the host of the picture; it wasn't showing up on the forum
Bear in mind, I'm not artist and haven't studied lighting in any detail. But, it seems to me most of the object would be in shadow. It may have an outline of light that is coming around the sides. The leaves would be quite bright because they are translucent so the light can get through. Maybe through the ugly smudgy edit I made, you'll get a general idea of what I'm trying to convey.