Dates...

Hey lovelies, so i had my doctors appointment at 5 weeks and my first ultrasound at 8 weeks leaning more towards 9 weeks. Durimg the ultrasound she said I'm only 7 weeks due to the size. Now what should I do? I'm 9 weeks today according to dates and what not but only almost 8 according to ultrasound.... What am I better off going by as I was planning on announcing as I've been a week ahead apparently....