No enough calcium which resulted in very weak curd.
You can add a tiny tiny bit of rennet (maybe 1\10th of what you would add in a rennet set cheese) to get a stronger set.
You didnt acidify the curds enough (did you get whey floating on top of your curd, you usually get that once your below 5.0 or so. your aiming to 4.6-4.
Final tip: once set, put the pot into the fridge, the curd will firm up.
Also also use two layers of cloth if it has open weave (like plyban)