If I remember rightly the Bell Gargoyle has quite wide sweeps with its weapon right?
I'm anti-shield but I think if you try to take the hit whilst shielded, you're going to be struggling to keep your stamina at a by decent level. You should be able to dodge around it so you're attacking it's best. Just don't get greedy with hits - get two in at most before backing away.
The overhead smash is fairly easy to avoid as it's so slow, and gives you a chance to get in. Eventually you'll learn the boss enough that you aren't just dodging away, but dodging in a way that gets you closer to it for a hit.
If you're having trouble, just go in to the fight with zero souls and nothing to lose, and practice avoiding his attacks. Very few fights are DPS races - though
in this fight, that will have its benefits later and instead if you can survive, you can usually live long enough to deal the damage. If you're consistently getting hit or if you don't know when it's safe to heal, you'll find yourself getting cut down.
Second phase:
The other thing is, if you're having trouble, the first half of the game is open-ended enough that you can go elsewhere and do some levelling first.