My opinion: He wants to get what he can before he jettisons you. You can take a gamble, with very poor odds I think esp if you have Infinite Revisions or Money Back or 100% Satisfaction on your gig as they are an insta-out for the scammer, even after the whole job is settled and paid. I think he always knew the job was undoable and wants you to fail after he gets what he can so he can take any work done (and sent to him) for free.
Cancel now, take the hit to stats and look for a genuine job with a genuine buyer. This does not give him anything and also prevents him putting any kind of review. You cannot get paid. I don’t recall you saying what this job was supposed to pay but I am not sure you will ever truly get that money (which is probably pathetically low anyway).
Complete the whole Job and Deliver, as in right now tell him “No, I will not feel comfortable sending incomplete work” (he doesn’t own this work yet as you are unpaid). Once you Deliver he can call Revisions, claim he doesn’t like the job and Cancel (after he has the work in his hand), accept and Review (which may or may not be positive), and still Cancel if you have the terms above in your gig.
You have to decide. My gut is pretty clear that this will never come out in your favor so the only way to have any control in this (messy) situation is to take everything away.
Either way, learn your lesson in how this got to here.
I feel for you, I really do. It is hard to find decent work. Just this week I had two people seem super interested until they saw the contract and realized that they would not be able to walk away with the work for free (my contract is firm ).
Let us know what you decide and how this goes