WhenI completed the turquoise, green and pink lonestar, I attached the corners, and triangles. Laid down the wrong side of my top, then with masking tape 1" wide laid down a stip to follow the outline of the lone star triangles points, corners, but before I did that I pressed the lonestar wrong side up and on top of the fabric which I was going to add as part of the top also wrong side up, and the iron left a noticeable indent mark I could see with the naked eye, then placed on the painters tape. I then removed the lone star, cut out the pieces I needed and patched it all together pinning and basting until I got it lay nicely. I added the bat underneath the star, but ontop of the flannel backing just to get it straight. Measured from side to side of the star and top to bottom, to be certain it was centered on the flannel backing. It was a challenge, and wasn't difficult.
It definitely would be easier to lay it on a full piece of fabric then baste it down or applique it down.
Best of Luck with your beautiful lonestar quilt project. Please post when you are finished.