There's a trick when sewing HST's together. I usually put a pin through the diagonal corner on the first one, then match it, pushing the pin through to it's pair. I've never found any other way to do it, in order to get them to line up. Otherwise, your points do not match. Good luck and be sure to post a picture when you're done.
I think this is what you were asking?
This is how I did it, for all 270 blocks -
http://www.quiltingboard.com/picture...t-t270594.html