Oh and I don't understand why you would spray baste AND pin too...sounds like extra effort and time.
I've been using the spray basting for years, that is how I learned how to quilt, have never pinned. It holds very securely. The only time I have some issues is when I have been extra cautious not to have 'over spray' at the corners and edges. Then it might not hold as secure, so I give it a quick spritz again, and all is good.
Definitely have to have a sheet or something under it around the outside of the quilt to catch the overspray cuz it will make floors tacky. I spray baste on my tile floor, definitely don't want to get it on carpet!
warm quilt hugs, sue in CA