Well, there are some obvious things in the reference that you didn't put in your version.
1. The hair - it's much MUCH bigger, and the curves you used don't really have the same effect as the sharper spiky-er texture of the ref.
2. The chin - he has an angled jawline and pointy chin, in your version it's very square... and even if you don't want to copy the style of the ref exactly, this is a big part in what makes the character recognizable so, I really don't understand why you made the chin so straight..
3. This is the biggest issue, I think, the eyes - even with giant hair and pointy, no one will know that it's Huey if you keep on this track when you do the eyes. He has an exxagerated forehead, and in the ref his eyebrow only goes up so high because of his expression. In your pixel 1. the eyebrows are both the same, which tells me you're doing a different expression on his face, and 2. The slope of the eyebrows is a lot less steep than in the ref.
4. His hair goes lower down his neck, which also should be a little thinner.
There is a certain delicate quality in Huey's features, and still, even this early on, I don't see that in your piece. All these things are fixable, but I'd suggest you start over on this before you put too much time into it. It just doesn't reflect the character well enough.
