If the batting said 2 to 4 inches, I would try for 2 inches just to be on the safe side. When I was new, I didn't pay any attention to how far apart the quilting should be and now after a few washings the batting has bunched up. I think you should err on the side of caution and with echo quilting around the cups, or echo quilt a few times around the background squares. That would be the easiest. Another easy fix is straight lines like the rays of the sun from the cups to the edge of the block about 1 inch apart. Your quilt is very pretty and all the different cups make it very nice. Good job.
Sue