4 x 4 huh? thats a big space to fill! But You impress me...really. Yeah I could critique the obvious, fingers look a bit wierd, eyes, not quite right etc etc, but I think It works this way. Prehaps, it adds more to the over all aesthetic of the painting, crooked lines, areas where its less well 'drawn' however...no, it does, (just took another look..) I like the way it looks, I always find a good painting needs balance like this, ying/yang if you will, some sharp areas, some messy, etc.... The compostion is really quite nice and the image works...square is a nightmare to compose on, but this feels natural.
I think that your work in this vain would benefit hugely from more paint though, I can see a fair amount of texture, but I can imagine this piece , or similar with tons of paint, lots and lots of great texture You have to be careful with stretched canvas as to how much weight you can put on it, but try mounting the canvas on board. I find a great way to add texture to oil paint is to mix in refined whiting, you may need to add more binder, oil, resin etc, but whiting will give you serious body and it goes off very quickly!, so you can build up the texture in a matter of days, even on something this size , then work cleaner oil paint over the top, you should still be able to remove the heavier paint if it gets in the way...sorry, I have gone into waffle mode.....but I really like this painting...you should most certainly keep it up, you have some talent there!
Dont fuss over the detail..there is enough here, Making it too photo-realist would kill the charm. Just use more paint!