Hmmm...I didn't know you could attach the binding separately like that. One learns something new every day. Thanks and good luck with the continuous binding, it's the only way I know how to do it, and from my experience if your top is square, your binding will be too. Just start in the middle of one side and leave a long-enough tail before you start stitching.
Here is a great tut
http://loftcreations.blogspot.com/20...-tutorial.html
Also, to figure out how much of a long binding strip you need, add the lengths of all four sides together plus about 10'', this way you have some wiggle room when you are joining the ends.
I hope this helps!