when to announce

Cat
I'm finding it so hard to keep this secret! When I had my first appointment with the midwife she put me one week ahead of what I thought, which would make me 12 weeks already, so I've been gearing up to tell everyone, and work of course.. - right after the first scan which was yesterday.. 
Low and behold - I'm 11 weeks like I thought, and so the baby was too small to run the screening tests so I'm booked in again for may 5- and so I feel torn between just waiting another week, telling now or waiting until may 5. I'm feel like I'm going mad..