Well, I did fix that one little square..I found a bigger piece of the fabric, so  I cut a small strip about 2 inches long and 1 2/5 inches wide.  Pressed the shorter edges a 1/4 inch...undid the top and bottum seams where the square was.  Slipped the prepared square into the two slots to cover the offending square...sewed the seams back up...turned it over and hand sewed the other two seams.  I examined it carefully and you can't tell where I fixed it!  GREAT..I gave it a good press...Now I am finding that when I press them seams open, I am disturbing the other seams that are pressed ...messing them up, so to speak.  So, I got my presscloth and started pressing all the seams again, this time covering the one I have done.  Worked like a charm...
I got the camera out to take a pic and then I noticed....another mistake...then another.  Well, I am going to use the same trick I just tried.  Hopefully it will work for a triangle.....We will see!
I really don't know how I did that...I was so carefull about the colour placement.  Just not careful enough, I guess.