Think of it like a miter from the wrong side....When you get to the point, continue the fold to the end of fabric, then turn it back unto itself to form the point, and it should all be nicely folded as you continue down the other side.
Man, I just reread that and I don't know if it's even comprehensible. But I don't know how else to explain it.
It's like you were needle turn appliquing it. Does that help?
Oy.