I was going to suggest you sit tight and see if anything comes of it. It sounds like nothing has, at least not yet. If your parents do ask you about it, I think the best thing to do is own up to it. Yes, Mom... I am an atheist. Just make sure she understands that it only means you do not believe in the existence of god(s). Eating babies is optional.
I am all for standing up for yourself as an atheist, I do it all the time, but I also feel that family harmony is worth a bit of sacrifice. If being open about your atheism will cause a serious rift in your family relationships, I don't think it hurts anyone to leave that subject on the shelf around them. That doesn't mean that you have to pretend to be a believer, but you don't have to 'rub it in their faces', either. Coming out to your family is always a difficult thing to do and the experience will be different for every individual. Good luck.
I am all for standing up for yourself as an atheist, I do it all the time, but I also feel that family harmony is worth a bit of sacrifice. If being open about your atheism will cause a serious rift in your family relationships, I don't think it hurts anyone to leave that subject on the shelf around them. That doesn't mean that you have to pretend to be a believer, but you don't have to 'rub it in their faces', either. Coming out to your family is always a difficult thing to do and the experience will be different for every individual. Good luck.