I know this is resolved - but I definitely echo what Jezz said about not seeming wishy-washy on how you feel and being upfront about the "no" answer.
I have some otherwise fabulous friends who drive me NUTS with their flakiness - if you don't want to do something, just say so from the get-go. I can't tell you how many times I've planned events for groups of people where a couple people just bailed last minute with excuses that made it pretty obvious that they were never planning on going. Or that said yes to vacation plans, then bailed last minute and left me with a half-empty vacation house.
(LOL sorry btw that rant totally sidetracked from this thread, and was not intended for you - just a bit of a rant that made me feel a bit better to get off my chest)