There's a little difficulty gap between the first and the second dungeon. I also struggled the first time. You have to replay the first dungeon and get some upgrades on your deck before you're able to beat the second one. Also, try to learn this tactic: leave at least an enemy on each turn, unless you can easily beat them all. You don't have to collect every gold, you can discard these cards to clear the round more easily. Finally, sometimes you can runaway after picking some itens and take some damage to get a new reroll of cards. I was able to finish the demo easily in 2 days. Hope this helps.