cant drop sacrificial heart

So in act 3 I picked up the heart before beating the boss and then progressing onto cruel, I then realized I had a quest item in my inventory and couldn't get rid of it or go back so now I'm in act 2 with a heart taking up 4 of my slots permanently until I can get back to that point... is there any way around this?

You can go back into Act 3 Normal and finish the quest there. Carrying the item to Act 3 Cruel and trying to use the heart there either won't work, or will create more problems.

Generally speaking, you can get rid of quest items by dropping them outside of town (ie any combat area). With the current state of PoE2, I cannot advise this course of action, because the quest may not function properly (you may not be able to find another Heart), and the quest rewards 2 passive points--which isn't a small loss.