Yes. Exactly. The thought was starting to grow in his mind and this to me has always been like a slip-up. That "Not yet".
I guess I can't argue that it's evidence of its growing power. But I believe Tolkien is in print as saying that none of them could have resisted its power in the end.
That's where some of Frodo's heroism comes in maybe, understanding the rings deadly power and threat, he still determined to walk into Mordor in pursuit of its destruction, if he could, in that way help the free folk of Middle Earth.