First of all, I like your style! The cross hatching on the shirt looks really good.
But, like you said some proportions are off. His face is actually the biggest part, but his body and top/back of his head are too small. Try to have the eye level roughly on the horizontal center line of the head. Your boy will need to bump up his twohead to a forehead. His neck is rather straight as well, and that makes the back of his head pretty small. The neck actually has quite a curve to it that leads up to the back of the head, it makes more of an elongated 'S' shape. Curve the back of his head out a wee bit more so his brain can have a little more thinkin' room. References really are your best friend for solving proportional issues.
The freckles that sit just above his eyebrow also look a little bit odd; they're grouped together and they don't blend with the rest of the freckles. The background is really rough and I can tell you haven't got to that part yet, but all in all it's quite a nice sketch so far.
The main issue is just getting the proportions right. I hope this helped! emotion_c8