I reposition the block until I am happy that the point where all six seams will meet is right on, then I sew it in place. 
Once I have all the blocks assembled I pressed the seams around to the back of the freezer paper. This did not need pins as I was mostly dealing with straight lines of fabric...no clipping and curves. Only three places need clipped...they are the places you turn a corner where there is no seam...the very top and far left and right blocks. Do NOT to clip all the way to the freezer paper. 
Once the pressing is done baste the seams down. Once again the knot goes on the right side of the fabric for ease in clipping it when done. 
The center of the tumbling blocks. Mark the center of your 13" background fabric by folding the square in half and pressing the center. Refold the other direction and press the center. The + mark is the center.
If you will be using a Straight Set when you join all your blocks to make the quilt top then match up the center marks on the background fabric and the Tumbling Blocks. Pin in place with applique pins.
If you will be using a Straight Set when you join all your blocks to make the quilt top then match up the center marks on the background fabric and the Tumbling Blocks. Pin in place with applique pins. 
