Technically, MM, you are right.
Nevertheless, I also have been using “gender” dating back to a hideous conversation in the late 80’s concerning a research design I had with my graduate advisor and department head, also a bully and colossal A-hole. To my surprise, and without thinking, the word “gender” popped out of my mouth in reference to male/female data. He took the moment to repeat my phrase substituting “sex” for gender, letting me know what’s what in the most lascivious and “knowing” way. I’ve used the term “gender” ever since. Note that this was well before “gender” was in common usage. PS: I’m no shrinking violet.
Well, no offense, but you reacted like a shrinking violet and that you continue to use a word that is “technically incorrect” shows you are still a little afraid of what others think. Most ordinary Americans have absolutely NO reaction to the word “sex.” It is the Stalinists on the left who have a problem with it.
Now, if you choose to use the word “gender” because you want to, that’s something else again.