Ultrasound drama

So I scheduled an ultrasound at a boutique for next week to find out the gender of the baby. I asked my hubby when I first made the appointment if it was ok that my Dad and step mother were there with us. He said it was fine. Now he is upset that they will be there and won't even talk to me. I told him that I've already told them they could be there and it would be very mean to all of a sudden say they can't be. It's just an ultrasound I don't see the big deal and why he is so upset. I don't want him ruining everything by being grumpy and upset the whole time. What do I do?!