First, good work on the freeze out.
I agree with Charlie - the plan B should have been spontaneous when you got there, also adds value to you that you can suddenly come up with good alternatives - like you're such a fun and active guy there are hundreds of things you can think to do (note: cinema does not count as fun or active ... or even a good date).
Telling her you had a plan B already means you've obviously been strategising this for a while - all power back to her.
Next: honesty... Certainly lying is not the rules of the game, but learn the difference between sincerity and low value pleading honesty (Which I don't think Charlie meant anyway). I've seen too many guys confessing too much, too early, in the sacred name of hollywood honesty... and it just backfires like a 1950s banger.
You can make your feelings and intentions clear, while still having control...
Finally, she's stringing you along? NO... no no NO..... NO ... hang on... NO
You are allowing her to string you along.
She is being a coquette. Get used to it, learn to love it in fact. But, do not let it dictate your actions. I love girls thinking they're stringing me along, i love it when they think they have control.. it's part of the process and part of the fun... and as i'm actually in control, it's a powerful frame to have (but complicated to explain the logistics of - part of its power in fact).
In any case, if you don't want her stringing you along.. do not let her. Take the power back. Go find other women, other flirts, other fun... enjoy yourself and make her one of a group that you currently have 'on-the-go'... string her along just as much. let the sexual tension build as you both power struggle, then let it explode happily
I think you stand a real good chance with this. Keep your frame, control, and senses... and begin the new year very happily