Does she really love me
This is a question to ask her directly. Away from public eye. Tell her to not think about any one else's feelings except her own. The best case scenario you will get a simple yes or no answer...but it will probably be "I don't know" as well and nothing much you can do there.
Do I still love her?
Same thing except now for you. The above question is something for her to work on and this one is for you to work on. My personally, I would rather be friend zone'd or downright rejected than ponder those questions for a lifetime.
Did she really mean what she said about me?
Well I don't know if there really was a dare of if it was a cover up for letting you down. Something she can only answer. As for the "nice guy", you're the only person that knows you best. Even if she did not mean it, the opinion of one person should not bother you at all. You know where you stand, not her.
My guess (and only a guess) is that the fact that she used false pre-tenses to first approach you. She said that she liked you in terms of the dare while not meaning it. But times can change answers like that...she might like you now or she may not. Either way, carrying something like that is a very heavy weight to carry. It's a very complex form of guilt hard to explain.
So what do you do from here? Move on. Take from what went wrong and gain experience. The big movie called life isn't over yet.