Hey reddit, how do I end this relationship?

Not sure if this is where I should be going for this, but I need advice and fast.

I haven't been in a relationship for 3 years (I'm at university now). Lately I've been yearning for a relationship with a girl. I have one girl in mind that I've been trying to ask out for 3 months, but I'm a shy guy and haven't brought myself to do that.

Two weeks ago, a friend of mine told me she had feelings for me. I said I didn't know what to say and said I'd get back to her on that. I've thought a lot about it, and decided that maybe I just needed a relationship. I liked this girl, we're good friends and she is pretty, so I decided to go for it the other day. We made-out and bonded a bit, but there really was no spark for me.

She's mentally way further along in this relationship than me, and with two weeks left in the semester and she's leaving to study abroad semester so we wouldn't have time to bond much more. I thought that maybe a "spark" would develop, and by spark, I mean I don't find myself caring for her anymore than a normal friend. In fact, I still find myself caring more for my other friends than her.

I know what I have to do, I need to tell her that this isn't going to work. But my question is how do I do that? I can't tell her that I don't care about her enough because she's a good friend. Do I tell her that I friend-zoned her? Because that's what's really happened.

Please advise!

TL;DR Got into relationship with friend, find out I've friend-zoned her, how do I end it?

UPDATE Just chatted with the girl, she's obviously sad that I led her on, but I feel better knowing that in the end I did the "right" thing by being honest with her.