I was watching this great tutorial https://www.youtube.com/watch?v=8Ididulfg9w for sculpting a t-rex with a background image, everything was fine until I realized that when I had stretched my original circle the mesh around the image that I had made was super thin unlike the tutorial showed (this can be seen at 10:38) .I went back and watched it over and over again but could find nothing as to how he made the circle stretch out out evenly.
Here is the comparison between my t-rex and the tutorial t-rex
http://i.imgur.com/0OmfEVw.jpg
http://i.imgur.com/QiWfix2.jpg
Sorry for any bad terms ect that I have used as I am only new to zbrush and any help is greatly appreciated 
Thanks.