It doesn't look to me like you achored your back good enough when you basted it all together. Did you pin or tape your back down first before you added the batting and the quilt top? I haven't found a basting spray that I like yet so I pin baste. I doesen't look like you basting is close together enough. I pin my backing to the carpet with t-pins to anchor it taut before I add the batting and backing and then pin about every 4 inches. Hope this helps.