After you sew the 2 pieces together lay it flat when the pieces separated.
You will see that I used a pin to help hold the first piece of fabric in place while sewing on the line.
This is what your unit 1 will look like from the underside of your paper. Both fabrics now have the right side facing up.
Here I have folded the paper on the line between the areas 1 and 2 and am trimming my 1/4 seam allowance. Some people prefer to trim the seam allowance on the first fabric before adding the second fabric because it gives a nice straight line to help you line up the second fabric with.