I was wondering if I can extend my backing fabric larger so that I can use that also as my binding.

Sure. That is a way of binding the quilt without using an additional strip of fabric. You might want to add a bit more and double the fabric for durability.

I have done this although I have to say that after getting Anima's binding miter tool I find that even easier to do that using the backing...

Here are some tutorials on how to do it though..
http://www.ludlowquiltandsew.co.uk/Q...f_binding.html
http://www.ehow.com/how_5091791_self...d-corners.html

if you want to

it is up to you you can also just use the fabric you have on the back and make your own binding separate from the back. (clear as mud?) I have done that before.

What I have seen happen over time is that the binding will wear and fray. To fix this -if you can - you have to cut away that part of the quilt and that will probably not be a good thing. IMHO, better to use the separate binding.

Go for it. Have enough to double it

you can, but i prefer the durability of the doubled binding.

Thanks you to everyone. This is a great group.