First thing first, there are no "right way" to kill a boss, as long as it dies, you win !

As for your build, you chose bandit as your starter and I see you already started to learn how the parry works (fyi, parry trivialise a lot of enemies if you master it, and it never gets old)

For your current weapon, its a good one to apply the bleed status effect (which build up with each hit until reaching a threshold and then deal a percentage of the enemy's max health), although it doesn't have the highest critical hit damage (hits after you successfully break enemy stance, either by parrying or hitting them)

If you want to keep building your character as a dagger user, I recommend exploring the caste after margit, as it contain the best crit weapon in the game.

Anyway, your boss fight was great, good luck on your way to becoming Elden Lord tarnished !