If your blocks are not matching up, make sure that you are cutting them the exact size. 1/4 or 1/8 inch off make a huge difference as you go along. When I need to cut several pieces the same size, I cut a strip across the entire piece of fabric, (folding it selvege to selvege then once again - making 4 layers) then open the layes to make just two, and then cut my next blocks.