can a 15 week scan be wrong?

We had an elective ultrasound at 15+1 and found out at our gender reveal it's a girl. I have this strong feeling it's not right. I've even had dreams about a baby boy. I am grateful and blessed with whatever we have. I also didn't get a picture from them of girl parts and even our DVD doesn't clearly show. You see lines for a brief second then baby moves. My SIL said she clearly saw it when she was watching at the ultrasound and she could see ovaries but I've heard those can't really be seen or are sometimes mistaken and they're actually kidneys. Anybody ever been told girl first then told boy at a later scan? Want to feel confident before I tell my two other daughters the gender. I have one picture but it isn't even a potty shot the profile even looks like a boy to me. Thanks!