Uh oh... I think I did my binding wrong.

I started with 2.5 wide, folded in half, ironed, lined it up with quilt edge, and sewed all the way around. I did the corners like in the video and how Jenny, FQS, and others do it, folded it over and sewed on... mitering the corners correctly.
This gave me a tight double thickness binding with no room to spare. There is no way I could have left a little bit of batting left to plump it up or it would not have fit.

The video above looks like she sews a single layer on and has plenty to work with. For you guys who have mentioned using less than 2.5...is that a single layer of fabric binding?

If it's to be doubled, like I did mine, should I use wider than 2.5 to begin with? (before it's ironed in half, that is)
Was mine super tight because of the flannel backing? I used a low loft batting.
Did I make a goof?