The mixture is still VERY wet after 1.5 hrs in fridge. ANy suggestions for thickening? There is no way I can roll it right now.

Probably has to do with the ripeness of your avocado.

To "thicken" it, I would add in some ground nuts (hazelnuts, almonds, walnuts..etc.). That will help bind them and make it easier to roll into balls.

Add more chocolate?