When I made my lone star I had to rip out and redo the middle section twice and it still volcanoed a little bit. In the end the volcano quilted out. I suggest doing a fairly long stitch length so it will be easier to take out if necessary. Once together if it isn't volcano-ing go over with your normal stitch length.
I didn't use any rulers to line up the seams I lined up the points of the diamonds that radiate out in the rays of the star.