Any suggestion on how to add density to the flowers?

That's mostly genetics if you are providing a proper amount of DLI and fertilizing effectively. the products that claim they make buds 50% bigger and stinkier have never proven any of these claims. Mostly just word of mouth of people to obstinate to experience buyer's remorse. Also, simple read the ingredients. it's basic fertilizer ingredients or somethng to benefit the biome around the roots. besides keeping it healthy and lots of light, we don't have much say in the outcome. It's the genetics that matter. You can polish a turd all you want, but it remains a turd. (not saying this plant is a turd, but the concept applies to all levels of quality) you got a ton of leaf - so either that plant has a predisposition or you need to crank up the light a bit. Doesn't seem over-crowded, but that's hard to say with a 2d image. overcrowding can result in lower light levels per cola and end up with more leaf than you'd have otherwise. if giving 35-40 dli, it isn't the light.

Bud density mostly comes down to genetics and light intensity. Promoting even canopies allows you to maximize your light, beyond that you go with stronger lights(to a point). Harvesting too early can have an impact too.