How can I get Firefly to generate according to my specifications, and not add stereotypes?

I wanted Firefly to create an image of a woman riding mountainbike down a steep, stony, rooty single track, and all of you, men and women, who actually ride mtb knows how it looks: standing position, concentrated face, helmet on your forehead, elbows pointing outwards, dirty clothes, rarely a backpack. I really tried to be extreamly specific about the color on the womans clothes, position on the bike, face expression and so on, and the outcome was a stereotype of a happy smiling woman riding with no effort at all, sitting on the bike like it's a Sunday walk, wearing the helmet like a toddler, clothing not in the colors I specified but instead, and without me asking for it, a f-g backpack! And it doesn't help to write "NOT backpack" or "remove backpack" in the prompt! And of course, when I change the "woman/she/her" to "man/he/his" I get more action and seriousness, (and still a backpack) in the image.

🙂

I am an amateur, but how can I get Firefly to generate according to my specifications and not add thing I don't want to have?