Just a question but what is it with manga like these and the need to add 'just kidding' to the end of a sweet quote? I've seen it in several of the manga I've read here today and in the past and I'm wondering why they add it.
Seems like shorthand to me. Basically they're taking the idea that she can't keep her feelings in check and says something that reveals her true intention, but she realizes that it's something normally frowned upon and is putting the other person majorly on the spot. So she plays it off as a joke in order to make an opportunity for both of them to save face and maybe preserve their friendship. then boiling that all down to basically one sentence.
I think stuff like that hurts a story, but the audience is so familiar with it by now that they just blink and accept it. To me it's much the same as stereotypes being used in place of character development like tsundere, for instance. It's storytelling shorthand when decompression would be more satisfying.