Your flash is too strong. It is blowing out the details for the back of the dragon. I haven't quite figured out how to get the white backgrounds perfect either, I end up lightening them in PS.
Alright, I'll keep at it! haha. Its kinda fun playing with the lighting. I'll probly be posting again after christmas! lol Hopfully this time I get it perfect. xD
Try pointing a light straight at the backdrop behind the dragon instead of on him to light the background seperately. I haven't had much opportunity to play with the white backgrounds lately, all of my stuff has been on location, but that will be my next method since I have two flashes now.