Uninvited Guests

My in-laws are well meaning, but can be quite pushy sometimes. My sister-in-law had a 3d/4d ultrasound with her pregnancy, and loved it so much she paid for one for my husndand's cousin as well when she was expecting. She offered the same to us, and we accepted. It's a generous gift and she seemed so excited about it. However, after she sent me the confimation email for payment of the gift certificate, she followed that up with " If you're having family there, I know (my husband's brother) would love to be there". I hadn't thought about having family there, no. I thought my husband and I would go alone and later everyone could admire our pictures and souvenirs. I guess there is a separate screening room, but still. So I told her I guess that would be fine, and then to be fair and make it less weird its now kind of an open invitation for family. It did cause am argument with my mother, who said we wouldn't have wanted her there if my pushy in laws hadn't started inviting themselves. Ugh. What was I supppsed to say? They were paying and I felt like it was rude to say no. In addition my husband said the reason everyone wants to go (which was a mystery to me) is to find out the gender when we do. Now I really feel stupid for not thinking of that, and hurt that we can't keep it to ourselves for a couple of days before telling people. We'll walk back out to a crowd of people already knowing our special news. He doesn't think I should be upset, but grateful that everyone is excited. I don't feel grateful. I feel like nothing about my pregnancy and my baby is MINE anymore. Really just hoping for some support here ladies, NOT more attitudes like my husband's who think I should just get over it.