That comment about him losing control wasnt in reply to your comment kyubisrage but to some other comments that have been made. I also agree that he hit the forehead protector but I just dont think it was from resengan as there was no visible resengan in Naruto's hand. Lastly i dont think that it is important to speculate the specifics of what Sasuke was going to say. The fact that he said, "Naruto, I..." tells us enough because it lets us know that Sasuke realized something about himself because fo Naruto. But yeah i think " I am sorry" would have been fitting or "I was wrong".