I read back what I wrote, and realized it didn't make much sense.
ok, here is my second go!
A shadow box has two 'back' parts to it. one is a black felt board that sits at the very back of the frame, and the second part is the back with the hooks to hang the frame.
I took the felt part and cut it down to fit just inside of the frame to give room on the back where the back of the pins will be sticking out.
Once the pins were put on with the backs of the pins poking through, I placed the felt board inside the frame, just enought to give ample room so the backs of the pins were inside the frame.
Then I put the hanging back on, and hung it up!
Huh, this would be so much easier if I had a picture....I hope that made more sense?!