A bit late, but here enters the chaaaaad of dating. Just kidding, but anyways here is what I see:
1.It was first time for both, so she could have had trouble relaxing or having deep convo, cuz this is now serious between u two and not just casual talk while at school. For some relationships it takes time for borth parties to get used to each other,but once it happens, it is awesome.
2.U were excited for the possibility of dating a girl, she caught ur attention, made herself approachable and now that u 2 have went on a date, excitement is lost, with dissapointmed being only thing left(u had some expectations, and they werent fulfilled). This is just how our brains work, this is what forces people to switch partners occasionally, this “hype” is really powerful, but lasts shortly.
It is good that u are the dissapointed one, cuz trust me it sucks when girl gets to know u, and then rejects u.
3.SilverZuzu wrote beautiful reply. But Philip as well.
This could be just a learning experience where u partially learned what sort of girl u wanna date.
But also, it could just be wrong timing and in a month from now u will be writting how u are together and how happy u are.
Dating should be fun and explorative, at the end of the day u have made a female friend, and girls automatically like u more when they see u talking to another girl. So at the end of the day, NOTHING IS OVER, u have lost what u wanted, but gained what u needed.