I don't know if I can explain this well enough for anyone to understand but here is how I do my corners. after you have sewn the first edge of the border on I press then turn over then stitch almost to a corner -pull the binding at the corner straight in then fold over the stitched side then the other side and the it looks like a mitered corner-the sew around till you get to the next corner and repeat.
Heck--I don't know if I could follow those instructions or not. Sorry.