Welcome to the best Quilting Forum on the 'net. Every quilt I make presents this problem. I try so hard to be accurate in my measuring and cutting and still I can end up "off." I've started lightly starching my fabric before cutting and that has helped so much and I take time to check myself as I go along with each block. Fellow member, lakekids, really gets it when she states "The only thing that matters is the size of the piece after its sewn."