I would remove the paper.
Then I would measure each unit to make sure the interior (center point) angle is 45 degrees, using an acrylic ruler and/or the lines on the cutting mat. Press them so that they are (or trim if they are not, but usually it's a matter of pressing). If they are not 45 degrees now, they will not be 90 degrees when you sew them into quarters!
Sew them into quarters. Measure that 90 degree angle and make sure it's perfect. Also be sure that the diagonal seam in your unit is on the 45 degree line.
Sew those so you have two halves and make sure you are working with two flat lines and that the center points you have sewn thus far are a good point and that they are 1/4" from that straight edge! At this point, you can pin through those centers and sew the two halves together.
BUT - pinning that many layers tends to be bulky. Lengthen your stitch length as far as you can and baste the seam (you can even just baste though the center 6" of the seam so you don't have to do the whole length at this point.) Open the seam and see how it looks. If it is a good match, shorten your seam length and sew right over the basting. If it is not right, the basting will be easy to pull out and do over.
Hope that helps!