It is two or section 2 or the one you have marked as 2.
Later on going towards 3, Macbeth states that he is haunted by his dreams, and he will no longer tolerate that.
But two is saying that they have badly wounded the snake, but they have not killed it. It means that he still thinks there is danger. Killing Duncan got him the throne. Killing Banquo should have assured that his linage would make sure that Scotland was ruled by his heirs and there heirs as well. That's when things began to go badly and he has suffered the nightmares of those who feel guilt.
He knows the job of murder is not complete and he is unsure of what will happen.