100% serious mode
Demon possession solutions that I think could work:
Solution 1:
Just say, "forget off demons" or something to that effect out loud or in your mind. Push them out forcefully and don't let them back in, this may require experience you don't have.
Solution 2:
Pray. Seriously works, If done correctly and with meaning, your body should heat up and God takes care of the rest. If you feel chills, that's bad. and I recommend you go to solution 3.
Solution 3:
go to your nearest Mormon church and explaining the situation, ask for a priesthood blessing. I'm sure they would be happy to oblige. (Mormon because they do these things for free as far as I know, just be nice)
In the future, I recommend not watching scary things or things that feel creepy/wrong.
This has been your friendly neighborhood Robo's guide to demon possession, if you feel you need more information, feel free to ask.