I like the little bit of shrinkage I get when a quilt is washed. I also like to use Hobbs 80/20 fusible batt for machine quilting. It is water soluable so if I washed it, no fusible which defeats the point in using it. I don't know why your batt has grown unless the hot water relaxed the fibers? I think you need to do a few experiments to see if it will shrink again. Cut a couple of 8 inch quilt sandwiches and quilt them with the same pattern. Wash one that you didn't pre-shrink/stretch the batt and one that the batt stretched in it. Re-measure them both to see if they are still 8 inches after washing and drying and go with what look you like best. Good luck!