Sounds to me like you've been Nice Guy'd. That sucks.
In case not all is lost, she may have been busy; but the best thing to do is ignore it and just move on. Associates/short-term friends only get 1 favor; any more, without anything in return for you going out of your way again (at least gas money for the trip), and you are a fool or a dogged good Samaritan (or THE designated driver). I nickname it the 'Guest' rule. Any more times, and they better start providing some support. Even moreso the more requests/demands come in without anything in return on their end, then no more help from you anymore (IE- You're no longer a guest in my books, get it yourself now. Whine all you want, but you used up all your privileges).
Kinda a reason I've become selective of who I help out and when I feel like being helpful, especially as an adult these days, compared to while I was in school where I was naive, seeing as this has happened a few times myself. Not worth the pursuit. In most cases, never worth it at all; besides the good feeling you get for being helpful in any other case. AKA- The consolation prize for being a Nice Guy. You can't fill a gas tank with that.
EDIT:
↓: Like I said, he got Nice Guy'd. Which in this context as well, if not for common reasons, being "white" is being 'Nice'.
Some wise advice: "Don't be a Nice Guy, just be a good person. If they can somehow tell the difference, you'd better as well."
And trust me, you'll soon be able to spot the truth really easily (Bullshit Detection 101), and can detect the same thing in women (Be they Nice Girls or good people) as they can in men. Being good knows no gender; 'Nice'ness is gender-specific, however; although they take different forms (male and female variants), they are essentially the same thing that causes disgust and disinterest that prevents things from going any further, even in same-sex pairs. Being nice is an illusion we cast on ourselves to hide our true intentions (especially from ourselves). If you're good, you have no need for it; and illusions can easily be noticed, even on other people (most easily by genuinely good people, yet eludes the nice). All but the one that's given into the illusion (usually oneself).
Kinda wish I had been given this kind of wisdom back then. Instead, I had to acquire that (as well as other) wisdom instead by harsh experience (AKA- the hard way), despite having tons of siblings that could've delivered it in those exact words.
Alternatively, you can always go with the good ol' Star Trek: First Contact line "Don't try to be a great man. Just be a man, and let history make its own judgment.".
EDIT EDIT:
Funny enough, she sounds like a 'Nice Girl'. Otherwise, she wouldn't have turned you down in such a manner. She took the wrong approach in a way that makes her feel better, AKA- The Nice Route; though not the right route. Instead of saying that she doesn't date your type (in this case: race) to let you off the hook easily, yet abruptly, she could've just outright stated she wasn't interested in you at all (no side-stepping with racial barriers), and yield a mutual benefit of both parties being able to move on sans worry. Silly as it sounds, in b4 "It's not that simple", IT REALLY IS THAT SIMPLE! The pain is short, but just enough to grow thicker skin and move on.
Oh yeah, and excuse my elaboration, but these are what I came across in my experiences, and am passing down just so you won't have to spend a few years trying to figure it out yourself. Just remember, nice people recognize other nice people and call them as such (most commonly nice girls calling out nice guys for being nice guys, but rarely the other way around), a good person tells it how it is, even if it has to be brutal honesty. As long as the truth is visible, and can be accepted by choice.