This happens to ALL OF US, all the time. Don't let it get to you. Remember a woman is nothing until she actually goes out with you. I had two women flake on me this week, granted I can't remember a time when it happened twice in a week, mostly because I forget about them as fast as this happens... but I have a date with a new one tomorrow, but I still have 24 hours to see if she doesn't cancel or just not fvcking show up. I honest to God do not care because there is nothing I can do about it.... if she shows up great... if she doesn't... no problem I'll have fun where I'm going anyway.
I get dead numbers and calls with no responses frequently. I forget about these almost has fast as it happens.
Some here are giving you advice on technique to improve your results... go ahead and pay attention, some of it is good advice... Me... well... I don't think you really did anything wrong... so what if you asked her if she had a BF.... so what that you texted her back too soon... heck, I've done these things before and sometimes it works, sometimes it doesn't... I do whatever I want... really.... sometimes I'm very direct sometimes I'm not.... it's really just a gut feeling I get at the moment for what I want to do.
What you did right was the most important thing, you saw a girl you wanted and you had the balls to approach her... you made your intentions clear, and you asked for her number. Most guys won't do that... so you are ahead of the game. Now the next thing you have to do is not let chicks flaky @ss behavior get to you.