The title pretty much says it all. There's a girl I talk to frequently and she definitely has potential to be more than just a friend. We talk regularly on the bus going to and from class and while walking her home and we have a lot of fun doing that. The other day I asked her if she wanted to do something the following day and got the reply she was too busy, and she was very sorry. (She truly was busy, so she wasn't lying at least)

I feel like I'm riding the line of the friend zone if things don't pick up soon. So my question is what's the best way to tell her/show her my intentions without completely losing her as a friend or making things awkward? Or if she doesn't want to progress should I not have her as a friend all together?