Since the batt is so thick you can't do a rocking hand quilt stitch. When that is the case you have to stab stitch which it sounds like you are doing? That is when you push the needle down from the top and pull it out the bottom and then come back up through the sandwich for the next stitch. When I stab stitch through thick spots on a quilt, I use my long pins around the area I am working on to anchor the layers together, this helps to keep the fabric layers from moving as I stitch.Since your sandwich is extra thick you may need long thin corsage pins to do the same? Try and keep your needle going straight down rather then at an angle.