Some girls don't want that "more muscly, and less clingy" guy. Really. You could be just her type. Perhaps she's shy, too?
I have a friend like you that usually gets told the whole "let's be friends" thing. He's a really close friend, and I had to do this to him. As much as it hurt me to have to hurt him, I got over that. And, he's working on it.
All I can say, really, is that I have a crush on someone right now. We talked like friends, and flirted every now and then. Nothing big. And I'd not have said a word about my feelings if he hadn't slung his arm around me that night to let me know how he felt first. Some people need that push. And one day a girl will want to be more than just your friend :)