I could never say enough about how magical the blocking process is! You can change the shape of a piece, simply by getting it wet and pinning it into the shape you want it to be- as long as the shape is similar to what you have crocheted. When the thread or yarn gets wet, it allows you to stretch it into shape, and establish a new memory to the fibers.
I was making a new Mini Masterpiece sample for eWoodStory, and thought I should document my steps to show you how I make granny squares fit into the rectangular frames.
1. I marked the holes of the frame with a pencil, onto a plain sheet of paper.
2. I crocheted a miniature granny square, using pearl cotton size 8, and a size 1.75mm hook. I crocheted enough rounds, so that the square was slightly wider than the width of the frame. That way it can stretch all the way from the top to the bottom and be the correct width.
3. Spray the granny square with water, and using an ironing board or blocking board as a base, pin out into shape on the paper pattern that has been topped with plastic to keep it dry.
4. Allow to dry completely before removing the pins.
5. Now the granny square turned rectangle can be easily stitched into the frame!