The Nun is a genuinely great movie which is kinda creepy. If you want to watch The Nun online free (the full movie) then here are a few options (we checked these as recently as January 2020):
Just cancel before the 7 days is up and you don’t pay anything ever, simple. If you’re wanting to watch films like The Nun online for free and in high quality right now, then a free trial with Amazon Prime Video is your best option.
There aren’t too many other options if you’re looking to stream the Nun without paying anything, HBO will shortly be making the film available on HBO Now, so if this happens you may be able to start a free trial with HBO Now and you’ll then be able to stream The Nun for free. But at the moment this is only a maybe!