Gender Reveal US Drama

Aj
I don't usually post my own topics and I chose the relationships room bc it's about my husband. I found out yesterday that I can go to a place that can tell you the gender at 14-15 weeks, so I made an appointment for today. My mom wants to come and she wants to pay for it. Then my sister said she would also like to come and since the place allows for 15 people to come, I said sure.
    Now my husband is mad that my sister and mom are coming bc he feels like it should just be the parents there and he's acting really childish about it. I'm struggling to see what the big deal is. He didn't even come to my OB appointment and there was at least one US with our son that he didn't go to so my sister went in his place. 
     What is so wrong with wanting my mom and sister to be a part of this experience? Especially since my mom is paying for it. They said the US would only take like 10 minutes and it's not like they're in the delivery room or something. Which I also don't think would be a big deal, but he's dead set against it. Now I'm going to have to deal with his attitude all day. Am I being unreasonable?