dont worry my new DJ, you are on the right tracks to get this chick.
Ok firstly girls nowdays are very busy, sometimes they are generally busy and really cant go with you or they are giving you the message to bugger off. If she has a geniuine reason and does say no sometimes it is totally acceptable, just dont keep calling her for a date, it will get her pissed off, my personal lines are max 2 calls per week, if i cant date her monday then i will call her on thursday and date her on sunday.
She invites you to go out, this is good, but you have to make sure you make a move soon, but not too soon, you see if you make a move too soon she will think all you want is sex, but if you take too long she will assume you just want to be friends, so its best to show her that you are attracted to her, but dont just shout out"i like you wil you be my girl", do it through body language, do some light flirting with her, talk to her with C+F(****ey and funny, if you dont know about it sign up to david's newletter or buy his book).
Practice your skills, read the hall of fame and quick tips, also make sure your life doesnt revolve around her, if you go out with her do something active like cycling or hiking.
Get the general drift? i cant explain everything right now, i got to do my biology coursework.
Goodluck and i hope you succeed