Although a good start, the problem that arise when looking at thisare quite troubling.
One thing that Ms Paint lacks is any real line quality and line weight. These are something that you really have to do manually in Ms Paint. With this single pixel line the thing lacks character and feeling.
Speaking of lines, it looks like you used a line tool over the entire thing rather than actually attempt to draw the lines. You could have at least tried to use the curve line tool, I mean it's not great but it is something bit better. What you have here seems so blocky and cumbersome.
The color is the next issue I have to address. The flat color and lack of shading really takes away from the piece. You should have added a bit of subtle shading and highlights. But a downside is that as simple as this is and with the line quality, if the lighting was done wrong it would utterly destroy this.
The hair looks quite flat as well and shares a lot of the same issues with lighting as the rest of the piece
you should study your reference a little more when working on a piece like this.
Keep practicing and if you need a better program, try GIMP