I used safety pins, I think about 200 pins but could have put them closer together if I hadn't run out. I thought it would hurt my hands but it didn't. I used the method in the video and taped 4 chopsticks to the table for the center. What an ingenious method - I never would have thought of it. There is some rippling on two of the borders but I couldn't face taking out the seams and the mitred corners so I just hope it will quilt out
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Thanks so much to everyone. By the way, what stitch length do people use for machine quilting?