Have you ever used rubber cement, Nyboy? It used to be a staple in setting up newspaper sheets. You put some on one piece of paper and let it dry. Then you can put it in place on another sheet of paper, pick it up and move it around until the paper looks right. The cemented paper is tacky enough to stick, but just like post-its, it can easily be moved or removed.
What I see is enough spray to make the mylar tacky. Put it on the ceiling. Add some molding around the outside edges to keep it from peeling or falling down. Should you ever want to remove the mylar, just remove the molding and gently pull the tacky mylar off the ceiling.
There's no reason to see yourself scraping for hours/days/weeks. Caveat: like rubber cement that WILL cement if used on both papers, that tacky spray will cement if sprayed on both the mylar and the ceiling.
But, hey! It's your shed, it's your mylar, and it's your decision. I'm good with whatever you are happy with. Staples would probably be the fastest and easiest to use in any case.