Re: Might have waited too long - need advice
If you have other things that come up, then you need to call her and tell her that you are sorry, but you cannot come. Then, you make plans for an alternate meetup instead of blowing her off like you did. That's how you usually cancel plans with a girl that you are interested in.
You also can't let the spark burn out on a target like that. If you are interested in the target, then you have to maintain the PUA essentials: flirting, messaging, meet-ups, everything. I would go on further, but I would then be reiterating everything that Kevin said.
"There is no better than adversity. Every defeat, every heartbreak, every loss, contains its own seed, its own lesson on how to improve your performance the next time." - Malcolm X