Consistency is the key. Sew a sample with scraps to make sure you are coming out to the correct finnished size. Try several. Label each one of your samples with precise notes so that you know what really works for you. Pressing is very important IMO. I press the piece as sewn first, then I press my seams open. To me, it reduces bulk as well as makes lining up next piece much easier. Your quilt will not fall apart in the wash even with these tiny seams! Typically everything overlaps so that all pieces are 'locked' into place. Even with open seams. It may be that you need to cut a smidge larger and trim for some or all blocks. Whatever works until you get there.