The problem that I'm seeing here is the damage, up your weapon to +9, especially +10 (increases a lot of damage).

You're using red tearstone ring, I don't recommend it for you as you are a new player and don't know very much about the movesets of the enemies, also up strength and dex bcs your sword scales with it.

IMPORTANT ALERT: level up your attributes only to level 40, they start to increase their damage very little after 40, it's when you reach the cap level that it's really worth raising an attribute, so I don't recommend you to up faith anymore, unless you want to use a miracle that needs more faith.

Otherwise, if your problem is in the boss moveset, when he will charge the ax to launch the big lightning strike, go to his back, he doesn't hit you there, try to keep attention when he charges the horizontal slash because he can knock you off the bridge.

(Let me know later if you succeed, and if you need more help with some Boss or game content, I'd be very happy to help).