Yup... Spray lightly then pin... Works 99.9% of the time. The good thing about the spray is if you notice slippage after a few days of working on the same projuct, just use your iron to press (not slide) the area where the fabric has turned loose and the spray is re-activated.
Good luck! Don't let it frustrate you, & PLEASE don't give up. The problem you are having is not uncommon, but easily fixed.
Hope this helps... If not, come back... We'll just try to make you laugh instead of helping you quilt. Some days, one is just as good as the other!! :D