Thanks...that would be me.
I just folded in the corners so the sides were at right angles to the front, sewed them by hand, and then cut away the excess on the inside. I think a pro would have separate pieces for the front and sides with piping at the seams. But that is beyond my abilities and budget right now.
But at least now I know the size and basic setup work well and it makes my riding way more enjoyable.
Brian