What is film rated?

I am doing the parental advisory feature for this movie's page because it hasn't been done and it really needs to be done. On the movie case it says not rated. But when I first saw it I heard or read somewhere it was rated R . I put in my report about the content . That this movie shouldn't be viewed by anyone under 13 . I think it could get by with a PG-13 rating .

At first , I didn't like this movie because it didn't jive that much with the first two movies . but I like it a lot.

I am concerned because about the rating I have had a few encounters with movies being too scary and having nightmares. I watched " Forrest Gump " when I was 10 - bad idea.
Please don't laugh , I couldn't go to the grocery store after seeing Forrest Gump's commanding officer without legs. There was young man at the grocery store who didn't have a hand. I would panic - my hands would get sweaty , I would shake and I would cry.
A few years ago , I saw the excorism of emily rose. Not only did I have nightmares , I had a psycotic episode.

So, I guess you could say I am an advocate for the Tv guidelines and the MPAA ratings.

Any pointers on the parental advisory feature would gladly be appreciated.