Fortunately, by doing my test sample first, I was able to make sure I had all the seam allowances in the right direction before I started stitching. I really think that was key in making the process work for me. Here is how I did the stitching but please be aware that I am Left Handed so I am stitching in the opposite direction of most people.
This first photo is going into a valley. You can see that the seam allowance is pressed towards the lighter diamond here. It should always point towards the diamond that moves up as you come out of the valley.
From here I would take a few more stitches and then loosen the stitches in that seam so the dark fabric can be turned under.
Now stitch right to the seam and I take an extra tiny stitch to make sure the stitching of the seam holds. Then start turning the seam allowance of the light diamond.
And start stitching.
Stitch to the point. You can see that the seam allowance on both sides of the light diamond point towards it. I found this was also better for stitching the point. Stitch right to the point making sure that you take very tiny stitches as you approach the point. This makes sure that the seam allowance does not push through when turning the point.
I also take a tiny extra stitch before tucking under the seam allowance at the tip.
Oops didn't get this close enough but I am turning the point here using the tip of the needle.
And taking a stitch on a newly turned point. You can see in the photos that I use the tip of my thumb to hold everything in place and use the needle to turn the edges under to my drawn line. I try to turn the edge so the line is then invisible but use a Frixion pen to mark the line so that if any marks remain they do iron right out. And here is a close up of the finished border.
And one of those tricky six petaled flowers. But I have no hints for making those points come together. I just needleturned them in place adjusting position if necessary as I went.
I am now looking forward to part 3!