It's very cute. You used the right colors. Her face does not look like the faces In the anime (Unless that's what you wanted to do). Also in K-ON, whenever they open their mouths, the teeth are showing.I would suggest that you do the lines (hair) with the line tool. You could also make the barrettes sand out by drawing them on top of the lines. But overall I like your drawing. You have talent so keep on drawing!~
p-s: If you want your pictures to look more professional, use a program like sumo-paint (0nline) and the select the white square/contour of your picture withe the magic wand tool.