Beautiful quilt top, what a shame about the back. It does look like a tension problem. It can be a drag to rip out all that stitching but if you have several quilting buddies it could be a good reason to get together to catch up while they help you take care of the unstitching. Provide some beverages and snacks and it will be done before you know it. Call it a "Reverse Quilting Bee". If I could help you, I would.