How much health do you have? I completed it with ~600 health.
If you have a shield that bashes, use it. Cleaving with the long sword is nearly useless (takes too long, only deals 15 damage against enemies with 60+ health).
If you have around 600+ health right now, but no decent primary weapon, I suggest that you save up for a sword like the Kithsteel Blade or higher. If not, I’m not even sure how you survived some of the previous levels (or you may have skipped those, I don’t know).
If you need gems, you could simulate games. The first few hundred gems come pretty quickly, though after a few thousand simulations earning gems becomes very slow. (More info here.) Or you could play the repeatable levels.