As the fight is beginning, Agunima will copy himself twice and this beginning animation takes quite a bit of time. Wait until the final copy is halfway or a bit more across the bottom to light the torches, then charge up a spin attack. You should only need to light the torches twice.
At the beginning, walk towards Gohma's shadow to make it fall down. Have feather and sword equipped and slash his claw, using feather to jump away when he tries to grab you, until it falls off. Then, equip slingshot with ember seeds and fire them at Gohma when it opens its eye. If you run out of ember seeds, you can use mystery seeds, and if you run out of mystery seeds, you need to kill Gohma's larvae and hope for seed drops.