When to announce? Please help!

I am officially 12 weeks today. Close friends and family know I'm expecting. I want to put it out to the world via Facebook tomorrow for New Year's but I'm afraid something will go wrong or I'll jinx myself...I have my NT ultrasound Monday and I'm afraid they'll tell me the baby stopped growing or something bad but I was at the dr this past Monday and baby's heart registered on Doppler close to 160 bpm...should I wait till Monday or announce tomorrow like I want? Not sure if I'm just being crazy...