Natsukage Floor Mattress Thicken Sleeping

The mattress has a hard rib down the center. I will give it the full 48 hours to see if this goes away. I thought I would need to use this product before now but didn’t so it stayed in the box. No instructions came with it and no notice on the outside of the box telling me to take it out as soon as it arrived. (I tracked down the order and info) If this is the reason there should be clear wording saying to remove upon delivery.