You should continue, it's good to get experience early! You're doing more than I was at your age, but I was still doing quite a lot. PayPal's definitely gotten a lot stricter since it opened.
I'm not very experienced with pixel art. I've got all the concepts of shading from doing non-pixel art, but I just can't emulate down to a pixel level as well as I'd like to. It's also hard to squeeze anatomy into such tiny spaces.
I added two more forms, and I think you should definitely keep the base. ovo~ It was made for you, and for practice for me.