Did you watch Sharon Schamber's video's - because, really, they're the ones that count. Here's part 1 of 3
http://www.youtube.com/watch?v=4PE0Yq9iGlc
Well, without seeing a picture...
Was the quilt corner square before you put on the binding?
Did you stop at a point, as you approached the corner, that was the same measurement as the width of your finished binding? iow, if your binding is going to finish at 1/4", then you need to stop 1/4". If it's going to be 1/2" binding, then 1/2" before.
Is the fabric for the binding perfectly folded in half?
Again, without seeing a pic, that's all can suggest about why you've got pagoda corners.
My guess it's probably got to do with where you stopped before the corner, but I can't say for sure.