Am I over reacting about this?

[คℓℓเє]

i think you are a bit egoistic. but then, what we deem important to us, may not be so to others. She should have kept your promise but you didn't, and it may lead to some embarrassing situations in future. Just ignore her now, unless she asks you something directly, then answer normally. Dont create a scene if you can help it. Or else, people may blame you instead of her.
Also dont do anything. Just leave it be! there's nothing you can do about this overly gossipy girl. You have already asked her about why you did it, and she has denied it. To voice my doubts, i think she's having a good laugh behind your back right now. Or maybe the girl you shared your feelings with may have told everyone, just like she told that girl. (Did you tell your friend to tell her, or did that friend did it of her own accord?)
I think if you look inside yourself, you will find the answer!