Trim the sides by lining your ruler up with the center triangles as in the pic below. Then continue to trim all three sides.
My section is straighter than it appears here. It wouldn't lay flat so it looks crooked but it wasn't.
Now add the white strips the same way as you did the dk ones.
Trim only the long strip at the bottom.
Make sure you don't trim the other sides as we will trim them after the block is all together.
Trim the bottom strip to 7/8" from the seam
Trim
[ATTACH=CONFIG]61255[/ATTACH]
Triangles trimmed
[ATTACH=CONFIG]61256[/ATTACH]
Add the white strips
[ATTACH=CONFIG]61257[/ATTACH]