[And if that isn't clear that he isn't necessarily coming to attack, his next words might be] Whatever it is that I have done to you, I am willing to pay the price to make amends - but do not punish Merlin for my own mistakes! [It's clear now that she has magic, and if he somehow said something to gain her mistrust and anger, like with Morgana--]
Or if he has done something to you, I will pay for his errors. But do not hurt him. Please... Whatever price I must pay to save him, I'll do it. Just tell me what I must do to spare him.