I see on the top left corner those pixels are smaller then the others and on mine the mouth is smaller for a reason.
Thats the original size. The big one is just scaled up. You're supposed to make them small and scale them up, not add smaller pixels to the bigger version. Sorry, but it just looks bad.
Like look at my avatar. All the pixels are the same size. I made it small then scaled it up afterward. How it should be...
And look at the 40 that I made on the OP. the small ones at the top are the original. I only scaled them up so you can actually see them...
/end rant