I think I might have been overboard with my words, we don't have to fight
Oh no, I've been struck !!
"The King, the King's to blame."
"Goodnight, sweet prince, and flight of angels sing thee to thy rest."
Hamlet realized that at the moment of their argument, it might have been out of hand & Horatio isn't convinced that Hamlet will actually win. Horatio thinks that this was planned all along and he is being set to fail.
Act 5, Scene 2, Page 281, Line 351 Laertes confesses that the King is the one who planned everything and that he poisoned the sword. Hamlet was set up to die.