I make my hourglass blocks just a tad big and then trim them. This ensures the blocks are both square and the correct size. The Ohio star blocks then make up so easily, without any need for stretch-and-sew.
The downside of this construction technique is that the trimming is rather tedious. I was wondering why it seemed so difficult, then I realized, I probably needed a new blade in my rotary cutter.
Wow, what a difference that new blade made! So much easier on the hands and shoulders when you don't need to press down with all your strength!
How do you remember to change your blade? For a while, I was changing it at the start of each new project but somehow, I got away from that practice. Must get back into the habit because it makes it all so much easier.