First off, you should be proud that you had the nerve to say anything. You should think to yourself, "Hey! she responded and seemed amused and intrested."
For most people (myself included) i have not yet broken my aproach anxeity.
Everything you say after that should be said with purpose and intent. Practice with yourself responses and routines. The purpose of which is to intially use but in an overall sence its like training wheels, they dont guide you they just give you a reference.
For instance, since i am new and changed my style of dress/posture/facial expressions, i have had alot of people say to me...
person: "Hey, you look good/healthy/handsom/cute...etc"
KA: " I feel good too, I think its important for people to reflect how they feel."
I respond with this slow, audibly and confidently....I mean it as i say it. however i could not use it for every compliment i receive...say...
person " WoW! i like that shirt it loooks good on you."
(notice this address's my changed apearence, but doesnt directly compliment me)
and here is were you adjust, you can go cocky funny, neg them, be honest..etc
Ka: "The price tag was bigger then the shirt"
or
Ka: "It'd prob look better on you, you workout more then me"
(said to a girl, preferably one who is fit, u dunt wana insult the fat chick )Ka: "I love it, i just bought it." (maybe add in something like "It's just cool enough that people will prob start mimicing me and go out and get one"...idk maybe some version of that)
Basically my point is that with everything you say you should be doing it to setup the next logical order of conversation. You opened her about the size of her headphones, regardless of her response (assuming a positive response) you should have had a neg or a story ready for her, as well as a time contraint, or at least have been thinking of it while she responded.
HB7 takes out headphones
Me: wow those are really big
HB7: Giggle*
HB7: Thats so you can hear very good.
YOU: "O I C! now that you mention it your ears do look kinda small." (big smile, look her in the eyes)
or
YOU: "Next week, i'll come to the libary and see you with 12" woofers strapped to your head..." confident laff/smile
then follow with...
YOU: "Hey I gotta go to (x,y,z) soon, but i gotta ask what your studying. You college types are smart, maybe i could learn something from you."
or
YOU: "I was just on my way to meet my friends..." sitting down..."but, i need some advice..." OR "but, let me ask you something..."
reopen the set, bringing things into your frame...whatever will let you start a routine or go in a direction were you have enough knoweledge to improv the conversation.
In any case this is just my opinion, let me know what you think, im new and could be wrong.