I'd watch out for the ghosts of Mary, Mary and Martha to haunt you!!!
Don't get yourself worked up too much about it - accidents happen. Spend a few more months looking for it, sometimes things just turn up. Have you looked on ALL of your meeting and ritual attire? I have often left my pin attached to a dress accidently only to find it a few weeks later (often not realizing that I lost it). If all else fails, you'll probably want to purchase a new badge. To my knowledge there is no rule about having to wear a badge to ritual so if you attend a few without badge, it's no big deal. I understand that you are new and probably want to sport your badge given any opportunity but don't let it bother you too much.