In most programs, it is very present unfortunately. You won’t likely be the only girl in a class ever, but in a smaller upper division class, it wouldn’t be uncommon to be one of 3-5. The percentage will be a bit higher in introductory courses, which also includes people taking minors and the class as a general elective.
Harvey Mudd has specifically tried to tackle this, and tries (and succeeds) at getting about a 50/50 CS ratio. Being a girl will actually help your chances there since they get many more male applicants. I would strongly suggest applying if you’d be interested in that environment, as you won’t find much like it anywhere else.
At this point, a lot of departments are trying to work against this, but none have been nearly as effective as Mudd. As you get closer to deciding on schools, it’s something to look into for each department specifically.
The industry as a whole suffers from this. This article is a good summary, but also highlights a lot of the bad sides of the field. Don’t let it discourage you, but it’s something that awareness can help with.
https://www.theatlantic.com/magazine/archive/2017/04/why-is-silicon-valley-so-awful-to-women/517788/