It's difficult to know what to suggest, without knowing how you're dissatisfied with the ship. The overall form is really strong. I think the parts where you've used light grey work well to break up the white, so maybe if you were to include a tiny bit more light grey that would help. I can't help wonder what the smaller bubble canopy would look like (but it looks like you want to fit a minifigure, so might not be able to do that with the smaller canopy). The fins sticking out at the back work well, as well, so maybe if you were to make them more pronounced/more of a feature that would improve the overall look.
It's all just personal preference, really, so hope you find something you're more satisfied with.