yeah the only reason I mentioned it is because of how an aquatic creature's tail is their main way of moving through the water, so it would need to be long to accommodate moving its colossal size at a decent predatory speed.
This is more loyal to the basis the Leviathan has in Jewish mythology, and other middleastern religions, a multi-headed water serpent, such as Lotan, the seven headed serpent. No mosasaurs or crocodiles here
Well he (and you) certainly did a good job. If we must connect this to an actual animal, crocodiles mating have been mistaken for sea monsters, and many trying to mate at once could create this effect, we should remember that before intensive hunting, crocodiles got a good deal larger than most we see now, something like 8 or so meters.
I love this take on the Leviathan. Definitely very terrifying, especially if you were able to see it at actual size! I just thought the mish-mash look of it made it particularly scary, and unlike anything we know, which is fitting.