Have them write down the gender in an envelope that you can take with you. Later, you can decide IF you want to open it. I have a friend who did that with #1...had a nice dinner with
DH and they opened the envelope...a big to-do about it. With #2, the baby didn't cooperate and they couldn't find out. In hindsight, she really wished they had known because she had a scheduled c-section with #2 and was very groggy/out of it so she didn't feel fully in-the-moment when they told her it was a girl. She would have preferred the envelope/unveiling method again.
So, I say, if you are in doubt about finding out -- go the envelope route and decide later.