Did you take your hours down to 12 to try forcing them into maturing? Getting as much good light as possible is one means of getting dense buds, especially with autos. They do look a tad leafy but that just may be these plants, you could defoliate slightly if you felt they're not getting good airflow. As for fattening the buds up, I think time will do this for you, I expect these plants have several more weeks to go, the recommended date isnt always so accurate. You could also be adding some bud booster like an astro flower, liquid karma, etc, or you can add 2 tablespoons of molasses to each gallon of water and that has necessary sugars that help the buds. The plants look healthy though and that's the most important thing.
