I can't put together any block without squaring it up, but in the video, Jenny doesn't square hers and some look quite off. I would think for that quilt to come out right, the blocks need to be 5 1/2". How many of yours need work?
Same machine, same thread, same everything and yet even a nine patch can be almost a 1/4" off. So maddening! I recently sewed enough 9 patches for a quilt and they were all small. I had used a different machine! They couldn't be used as the other block was snowballed, so I had to start over.