I'm willing to bet that no one saw. Is your dress a darker color? I also have to agree that someone would have said something to you if it were truly noticeable.
But now it's time to keep extra clothing in the office.
Don't stress. I'm positive no one saw or they would have told you. Right?? This is the kind of thing that even though it's uncomfortable, you can't not say something. What colour is your dress?