Hey.
Note that I'm new to this so this may not be the best advice, but here is my opinion.
You shouldn't have asked her to come out with you. You said "So, are we doing something special tonight?"
This sounds to me to lack confidence. In stead of asking if shes coming with you, you should assume that she wants to.
In stead, and please correct my game if I am wrong, you should have said something along the lines of:
"I am doing something special tonight, and I would like for you to be a part of that. What time can I pick you up?"
Then, if she asks what you are doing, say something along the lines of "You will find out when you see me." Or "Cant tell, its classified

I can only show you."
Then do something spontanious and fun that neither of you have done before, or do something romantic, like having a picknick in a park under the stars if the weather is right. I dunno, be creative
Pros, what do you think?