Did Macbeth mismanage his murder attempts?

Yes, Macbeth [c. 1014-August 15, 1057] mismanaged his murder attempts. In Act 2 Scene 2, he left bloodied corpses and bloodied crime scenes. In Scene 3, Macduff and Lennox stopped by to get King Duncan I [d. August 14, 1040] up and on to the next stop on the royal journey.

Macbeth showed Macduff the way to the King's room, but left Macduff to discover the three corpses. It was only when the King's sons, the subsequent Kings Malcolm III [d. November 13, 1093] and Donald III [d. 1099], started asking questions that Macbeth owned up to prior knowledge of the crimes. It was at that point that he stepped into the conversation and confessed to having killed the royal guards for having killed their sovereign. The situation was suspicious enough to make the King's two sons decide to flee England and organize opposition to their father's successor.

In Act 3 Scene 1, Macbeth organized the murder of friend and fellow General Banquo, and of Banquo's son Fleance. The three murderers succeeded in killing Banquo. But Fleance escaped. Macbeth had wanted both father and son killed, to foil the witches' prediction of Banquo's family line taking over the throne of Scotland.

In Act 4 Scene 1, Macbeth planned the murder of Macduff's entire family and household. He wanted to include Macduff among the casualties. But he learned from Lennox that Macduff already had fled to England. In Scene 2, the Macduff castle at Fife indeed became a bloodied crime scene of bloodied corpses. But news of the Macduff castle massacre only served to consolidate the combined opposition of invasion-minded Englishmen and rebellion-minded Scotsmen.