You're on the right track...to get that tail light housing and fender to fit perfectly will take some effort on your part. Fitting that part of the bike and making it look perfect is tricky. This is the type of detail that seprarates the men from the boys on a quality build. Spend the time on it...it will be worth it.
I see you have a hole drilled in the rear loop...are you running wiring or an additional both through that hole?
After you get everything fit to your satisfaction, I suggest drilling a hole through the bracket, rear loop, and fender to add a 10-24 bolt & nut to secure the fender. This will alleviate the stress on the encapsulated nut at the front of the tail light housing. I typically run my wiring through the rear loop also for a clean look.
Almost forgot to mention...remember that the two bolts low in the front of the fender and center bolt off the bracket near the back bone come into play. Don't just start tightening up botls one at a time...have them loose enough that you can move the fender around.