Spray Starch is your best friend in this situation. You will be amazed at how much fullness will be taken out. I spray my area that is too full until it is very wet. Let it dry. Don’t iron. If you need to give it a bit of a press when it is dry fine, but don’t get carried away.
Your quilt top looks very good and does not look like there is a terrible amount of stretching. The starch should work very well for you.
Ellen