Finding out the gender

I am 15 weeks, going to be 16 weeks on Friday and I've noticed a lot of people that are just as far, or not even as far as I am that have been able to find out the gender! Is it accurate this far? My last ultrasound I had someone that was pretty rude and just told me no, with no explanation to why they couldn't even try to see. I am so excited and inpatient to find out, I already have a little boy and have my fingers crossed for a girl! Also, we are trying to throw a reveal party and the sooner the better for us cause August is a crazy month for us.