Looks like you have an indica, so you have two weeks before the harvest window begins. During this time the buds will pack on 50% or more of their total weight. A lot of that will be in density.
CO2 will help give you dense buds, but its far from a requirement. Proper light distance, heat, pH, and nutrients will give you dense buds (assuming it's in the genes to begin with).
Don't get down, these ones you're running now may surprise you.