Heywood, lol.
OP... I only read the first couple of lines. Firstly, it took you a few weeks to ask her on a date? She'd have known from the start that you wanted to, and each day she realises that you're a little bit more of a pussy... cause you still don't have the courage.
Let me ask you something: after setting this date, did you keep talking online? My guess is that you left no reason for her to need to date you - she already knows everything and you'd have nothing to talk about, anyway.
Set a date, and do it properly so that there's absolutely no reason to talk to her before the date. If she initiates a conversation, talk for a little while (2-3 messages) and then tell her "I better get back to work, but I can't wait to see you!" or whatever. It's in the moments of silence that attraction is built through her being unsure of how you feel about her (
it is a scientific fact that women are more attracted to men whose feelings are unclear. Don't argue with science), and anticipating what the date might be (cause you've been mysterious and haven't told her - you've just told her to dress smart.

)
Imagine a song without any silence? It'd just be one constant noise. Wouldn't sound too good, would it? It's that silence that makes the music. Use the silence to your advantage.
^ probably the most dtrak comment I've ever posted, but you'll find that it's all right.
Edit: I'm sorry but I just read a little more and I still can't bring myself to get to the end of it. You're literally chasing her away. You did the right thing by trying to re-schedule ONCE. The problem is that she didn't give a counter offer, which meant that her being "busy" was a bullshit excuse for "I don't want to go on a date with you" ...sorry, man.
Time to meet some new women, so what are your plans to do this? Got a thread for new guys in my signature, but make sure you're doing what the last paragraph (I think) says; take action.