The question during the after movie discussion is class about, "why is there butch and femme," and the questions about masculinity and femininity seemed to me like we were asking, "why do we stereotype?" We can speculate but no one really knows why. I guess so we can generalize and make things more consistent. That way it is easier for is to talk about and to understand. Generalizing too much about anything can cause issues when talking about topics in depth. But I guess that's what makes butch and femme important is just that, that it needs to make more sense to the general public. They can understand that these are two lesbians having sex, but I feel like maybe that isn't enough for them. They need more roles to be filled for them to understand the scene better. They need something they can identify with. Men will identify with Corky and women will identify with Violet. As for masculinity being represented in a scene where two females are having sex, we could probably argue that the tattoo you see helps Corky seem more masculine. Also, we see Corky has a lot more muscle definition where Violet is more "round" and soft. I think the character placement and the way the camera moves enhances that this is a lesbian scene.
The trucking/panning shot that runs up their bodies helps the audience a lot. We see Violet's hand in Corky and when the camera moves further up we see breasts on top of other breasts. If they were in a different sexual position that maybe a man and women would be in, we might not see these shots. But I think the way everything was composed really enhanced it.