I got a legal opinion wrong because of my boss. What should I do next?

I wrote a legal opinion for another department of our company. I took it to my boss to see before sending it out and he said “just add this one thing in it and send it.” I added that one thing and that is the particular thing that was wrong. I had a gut feeling he was saying the wrong thing but I just trusted him. Now I’m kicking myself. Now it’s been referred back to me and most probably, my boss will not remember making the faulty suggestion. I’m very particular about my opinions and I am feeling terrible that I didn’t trust my gut with this!!!! GNAR!

Should I bring it to his notice that he told me to add it? Or will that look petty? How can I go about this?