Firstly, I agree with you, it does seem like really bad luck. But saying that... it doesn't seem like there is that much you can do about it now.
Secondly, don't listen to other guys who think you should be only interested in sex at your age! Its fine if you are, as many guys your age will be mainly interested in that and not much else, but if you're not then thats great too! I say, don't bow to peer pressure!! If you are looking for something else in a relationship... i.e. a girl you really care about, can have a great time with and get on with in many different ways... then I say keep looking for that and don't give up hope!
I know you're disappointed.
But sadly, it does sound like the chances of you meeting this girl again are slim to none.
However, there are plenty of other great girls out there who would love to go out with a more sensitive, more respectful guy like you! Because I tell you, in your age group those kinds of guys are hard to find!
So to conclude, I would say don't change who you are to
"fit in with the crowd" or
"seem cool" or
"because you think you should" ... do what seems right for you!!
And even though you've been unlucky and made a mistake this time, you've learnt from it and there are plenty of other great girls out there yet to meet!!
So don't give up looking!! You are very young so you have plenty of time to find that special someone.
Good luck!!