I have made several OBW and lining up carefully with a pin is so important. I pin very carefully and am careful not to move it. When it is all pinned I shake a bit and do check to make sure the pin is in the exact place in all six layers. I don't think I could cut in layers of three. I would make sure that blade is brand new. I am going to be cut a OBW probably next week and that is what I will do. I love, love them. I am making one for a friend for her birthday. I think I will be very busy, but really having fun putting the blocks together.
Also, don't forget to press the seams open.