Ok, sounds like I didn't really screw anything up and it's just part of the game. Thanks. Peeved me off because it happened right when girls night out was planned.
Girls Night actually seems to be the least thing you need to worry about.
According to my experience, Melissa and the other girls take you for a girl at the girls night, no matter how masculine you look.
You need to worry more about your job. When you work at Hooters and already have the promotion to work as waitress (instead of the kitchen), you have a chance to get fired when appearing too masculine (it is still a matter of chance ... according to my experience, the chances are rather small, that your boss sees you (while appearing male) and fires you ... but the chances are there.
Likewise, when working at the Boobies Bungalow in the Red Light District there is also a chance that you lose your job, when appearing as masculine.
Also, of course, living in Fairhaven has a certain chance that the creep at the reception desk discovers that you are not a girl and may blackmail you for it
(same goes, btw. when he discovers that you are snooping around in other girls belongings during maid duty ... it opens up another storyline where he lets you wear a maid outfit from the sex shop ... which, on the other hand, opens up another storyline where you get prostituted as sexy maid to investors of the home CEO)