Now that the shortened pearl pins are holding the diamond wrap band in place, you can pin the back in place with a little bit longer pearl pin.
I cut a pin longer than the front pins, inserted it into the back and bent the pin slightly forward. This part will be hidden against the back of the lapel.
You can see a better front on view of this bent pin.
I used scissors to clip the excess diamond wrap off the back.
I then inserted a second (shorter) pin in the back to securely hold the wrap in place.