It was actually very simple and I am by no means a seamstress. Do I know how to use a sewing machine? Yes. Do I have anything more than one needle and one presser foot? No. So this is beginner stuff.
I decided I would simply re-round the corners to get the frayed edges inside of a seam. First I decided to cut off the plastic edging. It wouldn't be necessary once the corners were inside the corner seam, and they would just get in the way when I was sewing. Here is what it looked like after I cut the plastic off
I transferred those points onto the inside fabric with pencil (this is hard to see from the pic, but its on the white part). This helped me remember what points needed to be included in the seam.
There was some fraying on the bottom of the backpack straps as well, but I decided to leave that alone. I wasn't about to cut the straps off and resew them back on further down. I also didn't was to tear open the bag to accomplish a reattachment properly More experienced sewers might be willing to, but I'm more inclinded to wrap them with a solid fabric to hide them. That's for another day : ) Just wanted to fix the obvious beaten corners.