This is too loose, right?

This is my first bind. Obviously, my text block is pretty big. My concern is that the signatures still shift around quite a lot, as seen in the second photo, and the gap when they are opened seems too large, as seen in the 3rd photo.

The only piece of advice I've seen on how to tell if your stitching is too loose is to tug on the loop of thread inside the signatures, and if it snaps back taut, your stitching is tight enough. Mine snaps back taut, but I feel as though that can't be enough of a measure due to the concerns I listed above. Thanks for any input!