Here are a couple of pictures showing how to line up the half hex's before sewing. This may help you out :D:D:D
The first picture shows the hexs right sides together and I have pins stuck in the 4 little triangle tips.
The second picture shows the hexs lined up, notice the little triangles on the upper left and right ends match up, where I have the pins stuck into them. The two tips in the center stick up, but don't match to anything.