How should I handle this???

My husband and I are 15 weeks pregnant. My next appoint is May 15th. I’m expecting them to tell us a gender. The thing is, his sister wants to throw us a gender reveal party and doesn’t want to throw it until June 29th! We are already anxious to find out and I don’t want to wait that long. Would I be in the wrong if I told her that we no longer want to have the gender reveal? BTW, at this point, she hasn’t spent any money, so she will not be at a loss. Please help.