I use 505 as well--the only difference for me is that I securely tape the backing down to a hard surface--spray 1/2 of batting and smooth/press it down then repeat with other half--then lay top down on the 2 pieces and repeat with the spray doing 1/2 at a time. Really smoothing and pressing as I do it. Possibly not using enough of the spray??? I usually check for bonding before removing the tape. Plus I then take the quilt to the ironing board and press it on both sides-maybe that helps?????