you know once it is washed no one will even notice if those lines are straight, the idea is to (quilt) the layers together so they do not shift, you do not have to do an x, you can run a wiggly line down in one direction anywhere, then wiggle a line across the other direction, so everything is held. i usually just use a decorative stitch and make it easy; one of the great things about rag quilts as they are fast and easy, you do not need to be so precise as to mark your squares, relax and have some fun with them :)
you can get some really fun great designs when you get creative with raggy quilts, be adventerous, it is the easiest method to experiment. you are still getting practice stitching, but you don't have to (sweat the small stuff) because when it gets washed it will not be noticed!