If it was the first run it could not have been a PG-13. Jaws came out in 1975 and the first PG-13 rating was Indiana Jones and the Temple of Doom in 1984.
That might be technically correct but I distinctly remember a recommendation that children under 13 be accompanied by a parent.
It was PG rated, and there were complaints about that, but the studio had too much clout for it to be rated R.
Red Dawn was the first PG-13 movie.
Wolverines!