Nice! - It could help to think of the movement of the parts of the face when designing your caricature. Capturing the expression is part of capturing the likeness. When I look at the reference, I get the feeling the the corners of the mouth are being pulled up and out. They push up the cheeks and it feels like they together with the eyes dive in toward the nose. In your drawing the corners of the mouth go down instead. Just like when trying the capture the pose of a figure, it helps to imagine doing (or actually doing) the expression yourself. What does making the expression feel like. Is your drawing expressing that? I hope this helps :)

great job!