I started to sew the hexes together in a row (no set in) edge to edge and back tack. Then I lined up two rows to make sure the placement is right. Now the sewing is very important at this stage. Sew from the beginning of the first side and just before you get to the seam line, back stitch. In other words, do not sew over the seam. Now, line the other side of the hex up and sew from the seam line to the end and so on.
Now finger press all the seam in direction they want to go and the press the back and the front.