I don't think that is his problem. The problem is that the rendered texture is in a 1:1 ratio (it's square) where the screen is a 4:3 ratio. This means that the sides will be stretched.

You have to change the texture transform matrix to use a 4:3 ratio:
m11=1.25
m22=1

I'll take a look at the code and show exactly how this is done (that isn't the actual code there) if I find some time in a little bit- unless someone beats me to it

-Rhuarc