I couldn't open your picture, but from your description I would suggest that you put the borders on and then trim them as little as possible to make the quilt as near square as you can get it without major cutting.
It is so very important that you sew exactly 1/4" seams on every seam. That is the only way you can be sure that everything is going to come out square, and you won't lose your points. If you are a little off, you can fudge a bit on the seam so you don't lose your points, but I don't recommend doing that throughout the block, because it will cause the whole thing to be off.
Good luck, and I hope you post a picture without the "save source" or whatever that option is when you attach the photo. I would like to see the block!! :-)