c'mon man this one is obvious - she asked you out, and then you waited a few days to ask her on a second date. From her point of view you have all the leverage; she already went above and beyond asking you out, and you make her wait a few days to reciprocate?
What do you think happened the next day? She starts chatting with her friends and mentions she made out with you. Her friends then proceed to tell her to slow down and "make him work for it", which makes her feel like she was acting like a sl*t. So what does she do? She overcompensates by shooting you down for a second or third date. She got it all backwards really - but this is why girls don't usually ask guys out, they tend to f*** it all up.
Thing is this can be fixed really easily - because since the girl asked you out in the first place you know she's attracted to you. She's just trying to get some leverage and self-respect back. Ask her out one more time casually and if she shoots you down then forget her; the ball is in her court at that point and since she is attracted to you she is likely to come around. You don't want to come off as needy or desperate, but if you play it off casual then you'll be fine.