I had a problem figuring out the "layering", "turning", and "basting", until i figured out it is done in that order. But no one has said how to do the layering. I have been doing this since the 50's. Talk about old! You need to place the top and back right sides together. The batt probably goes next to the top. If you want to baste at this point, that would be fine. But then you sew all around the outside leaving a few inches open for turning. Then you need to remove the basting in order to turn it.
Another way that we used to do was to sew just the top and back together, right sides together, leaving quite a large turning space. Turn it and then work the WOOL batting inside, trying to get it into the edges and corners all around. Doesn't sound like fun, does it. But we did it. Then they were tied with wool yarn. These quilts were not washed. If the top got too soiled, you took off the ties, opened the last seam and washed just the top and back. If the batt was bad, it went to the woolen mill to be recarded. Our quilts were not made for show, just for warmth.