No, the Septuagint is a Greek Translation of the OT, and it contained more than the First 5 books of the OT. It contains 47 to 49 books [3 and 4 Macabees].
No examples of anything from the OT survive save the Dead Sea Scrolls which date to 150BC, and those findings contain 3 of the Deuterocanicals, 2 of which were written in Hebrew, Tobit and Sirach, and Baruch was written in Greek. So the Jewish Community who translated and read the OT translated in the Dead Sea Scrolls.
Does it seem likely that the Dead Sea sect were mainstream Jews of the time?
Is it possible that the caves were also or previously a genizah for the storage of erroneous texts that contained the name of God?
What do actual Dead Sea Scroll scholars who aren’t theological partisans say about the texts concerning the Septuagint?
Could there be other erroneous Bible-like writings like there are rejected “Gospels”?