I don't want cake on my birthday?

I'm dieting trying to lose (I should say struggling) to lose my last 15 lbs, my birthday is coming up soon, I politely requested my family do not get me a cake (I'd rather be treated to a mani and pedi but I'm not going to make any demands), my mom says she's going to get one anyway (because no means yes ofcourse). Does this mean I'm obligated to eat it? Would I be rude if I still didn't eat it because I told her well ahead of time to not get me one? Thanks