Yes, there is enough HP to complete it 100%, and no, there’s no max to exp you can have at once. I suspect the problem you had is that you used the heart scrolls too early on. Since they always refill you to max HP, they’re worth a lot more if you hold them until you have higher max HP. In particular, if you get to 0 HP and you have enough exp to level up, you should always do so rather than using a scroll.