I know that most of you are familiar with this, but when you trim a square with triangle pieces in it, you can't just trim it square. You have to make sure the triangle seams in the block line up with the triangle line on the ruler. That is the most important step. And if you have other seams too, as in the Boston Block or the one you are making, keep an eye on those too. Look all around the outside to see if your points are where they belong. It's not hard, just time consuming.