What does Macbeth do that was not in his and Lady Macbeth's plan in Act 2 of Macbeth?

Macbeth takes the daggers with him instead of leaving them with the bodies.

Macbeth wants desperately to be king. It was an ambition sparked by the three witches, who told him of a prophesy that said he would become king. When the king’s son was named his heir instead, Macbeth was upset. He decided to take matters into his own hands and kill Duncan to take the throne. 

Macbeth wrote a letter to his wife,...

Macbeth takes the daggers with him instead of leaving them with the bodies.

Macbeth wants desperately to be king. It was an ambition sparked by the three witches, who told him of a prophesy that said he would become king. When the king’s son was named his heir instead, Macbeth was upset. He decided to take matters into his own hands and kill Duncan to take the throne. 

Macbeth wrote a letter to his wife, Lady Macbeth, telling her what the witches said. She was thrilled, but she never felt he could pull it off. As far as she was concerned, Macbeth was too full of “the milk of human kindness” to successfully carry out the plan. She would have to push him along.

Lady Macbeth developed a plan to kill Duncan and frame his guards. His sons would then flee, assuming they were next.  Macbeth has second thoughts, however, and worries that they might get caught. He has recently come down with a bout of morality and started to question the plan.

When Macbeth asks Lady Macbeth if the plan will fail, she scoffs at him and tells him to be a man.

MACBETH

If we should fail?

LADY MACBETH

We fail!
But screw your courage to the sticking-place,
And we'll not fail. (Act 1, Scene 7)

She outlines a very specific plan for him to follow, feeling that if she does not tell him exactly what to do he will mess it up. She tells him to wait until Duncan falls asleep, after which she will drug his guards. Then he can sneak up and kill Duncan. Part of the plan is to leave the daggers with the guards to incriminate them. Macbeth gets so flustered that he forgets that step. 

Why did you bring these daggers from the place?
They must lie there: go carry them; and smear
The sleepy grooms with blood. (Act 2, Scene 2)

No matter. They just tell everyone they found the bodies and Macbeth stabbed the men out of rage. Both of them do a superb bit of acting. Macbeth pretends to be overcome with grief, and Lady Macbeth faints from fear. Malcolm, Donalbain, and Macduff all buy their act completely. Why wouldn’t they? Macbeth is supposed to be a brave and noble lord and well above suspicion. Who would murder the king in his own house?