I wish the actual picture was closer to the scale of the preview. You wouldn't have nearly as much dead space (like the wall behind you). You could make it more interesting by adding more shading with the gray you already have in the picture to your skin, the door, the wall, etc.

 Looks pretty cool.

I did accidentally save it as a .jpg and I didn't know how to fix it.

Everything else I do is not nearly this big, but I wanted this to just be pretty giant.

You may want to start with a way smaller canvas, like 100x80 or something like that. This is unnecessarily big.

About the colors, well, you have 1257: http://hivemind.in/pj/specs/index.php?urls=http%3A%2F%2Fwww.pixeljoint.com%2Ffiles%2Ficons%2Ffull%2Fpixil_me.png

Even one brown pixel! Maybe at some point you saved the image as .jpg and the reduction added a lot of unnecesary colors. Always save it as .gif or .png