That looks quite nice. I presume you cast a real ribbon in clear resin? I'm planning to use segmented acrylic to mimic service ribbons when I hear back from the DoD on permission to use military emblems. Does the material in the lower blank have some tie-in to the ribbon?
The centerband piece looks good. I know (from experience) that it is the most difficult part of the case to get square and true.
If I were doing it, I think I'd cut the nib section of the case a little shorter, and lengthen the material in the lower barrel to match the upper barrel. To my eye, that yields a more symmetric looking pen. I also would use a bullet for the nib, rather than a kit nib. But, those are just personal preferences.
Good job,
Eric