Looks really good, but I think 138 colors is far too many for something like this. Try choosing a palette before starting and then just work from that to reduce the color count.
It seems like this was originally made as a smaller size, 40x40, but was scaled up to be 100x100. Because the new size is not an exact multiple of the original deminsions, such as 80x80 or 120x120, some of the enlarged pixels are 3x3 but some are 2x2, 3x2, or 2x3, which gives it an odd appearance. Is there a reason you didn't scale it proportionally?
You've got a few more colors than necessary- at least around the pinkish area. The background also has too many colors, as well as the shirt. Facial structure is pretty good, but the head looks kind of chopped off- maybe either curve the forehead back or make the hair taller.
The pixels have been stretched and lots of colors somehow added. Please resubmit at 1x, or at a resolution that does not stretch the pixels (such as 2.5x)