It can be difficult to line up a pieced back, especially if you want something centered. A good idea is to place the additional blocks or seams off center so you are only trying to line something up either top to bottom or left to right, not both. What I have done is use thumb tacks. Put the tacks thru the points in the back that you want to align. You can cover the heads with masking tape to keep them in place temporarily. Put the backing down, CAREFULLY smooth the batting on. Then again, CAREFULLY layer the top, using the tacks to align the places on top with the backing. when the sandwich is complete, remove the tacks.