AITAH for getting "too excited" at a photo session?

My friend's friend is a photographer, and she looked for a female and a male model to take a photoshoot for her portfolio. It was an intimate shoot, but there was no nudity at all. We were wearing masks (vienna style), she was in lingerie and I was in a suit pant and an unbuttoned white shirt. Actually it was very stylish.

It was my first time in this situation, but everyone else seemed more professional. The girl was very attractive, and at some point I got hard which and it was visible through the thin pants. The photographer noticed it of course, and she stopped the whole shoot. She pointed out that they are waiting for me, and it was extremely humiliating. But the girl looked at me like I was doing some horrible thing. Is it really an inappropriate thing? I know it is, but I can't control it, and we were shooting a hot scene, of course I got hard. Am I the asshole? What should I have done?