from the looks of it , its quite ok.
but the front tooth looks like its about to drop off, could use some adjusting
also it would look nicer if the ear shown some sign of depth.( according to the references mouse )
well something like this , but well u should change the color to your liking, just showing u what i mean
hmm as mention by the person above me , might be better to use a different outline
its quite decent for yoru first pixel art, keep up the good work