Not sure if it would help or not, but rather than pinning to your carpet, is there a flat place you could tape your backing to? I either use a floor for a smaller piece, or push several tables together to baste a larger quilt. I tape my back to the tables, starting in the center on each side, and then working my way to the corners, alternating sides a few pieces of tape at a time until all is taped down. You don't want to stretch the back too tightly when you tape-you just want a back that is nice and flat. Then I add the batting and smooth out with my hands, and next the top-which is well pressed. I start pinning in the center, smoothing out the quilt with my fingers, and pinning out about every 5" working out in each direction . If you don't want to pin baste, you could thread baste, but also working center out. Hope this helps.