Now is a good time to fix before it is quilted. Yes, you can take out as little stitching as is necessary - just the sides and the bottom plus two inches on either side. Sew the sides back in first after you flip the offending block (make sure it's okay - you have no idea how many of us make the same mistake over again), then sew the opening across the bottom of the block including the extra. Your seam ripper will become a good friend as you continue in your quilting. Be sure to post a picture when you are finished. We love pictures!