Even though I'm not a teacher, this has similarly happened to me. When I was first starting out, I literally needed to excuse myself from the room at the smell of anything warm and chocolatey/sugary. Now, three months in, the bother is much less because I learned to ignore it
Don't worry! One cupcake will not shatter it all. Just get right back OP or just eliminate some other stuff. I tend to eat lightly during the day because I enjoy having an ice cream cup after dinner.