You're fine....just continue to be the ideal man with girl B.
Lesson learned about online dating..girls treat it like a restroom....they do it in groups. So when you are hitting up several chicks on a site, chances are good a couple are friends.
This has been true two times in my past. One girl I hooked up with told me I had also emailed her friend online. We had a couple laughs on that. Another girl said the same thing, that her girlfriend and I also had a few emails at one point. For that reason alone, never bash a girl online or act the fool. Word gets out.