It looks great but I see you didn't knock down that little lip on the front section so it will screw in all the way. Just put a spacer inside your 10 mm mandrel so the front section just threads on a bit and use a thin parting tool to knock that shoulder down. Turn slow as that plastic is quite sensitive, polish and you're golden.
took a peek at yours...dopeI like it a lot! I made similar pen recently. Simple black is the exactly I was aiming for. http://www.penturners.org/forum/f13/kitless-2-3-a-106391/