Got rejected by a girl...?

so todaay at this restaurant when i walked in to buy somthing i got in line so i can pay at the register and the register girl looked at me n kind of gave me a smile. another cashier opened and then the cashier that kept looking at me asked me if i went to a her friends party last night and i said no, i dont know how she is. n then she said r u sure cus i remember i saw u. n then i told her nopeeee lol. n shes like smiling like it was me. so then i im about to leave i ask for her number cus i told her i mite know who she was talking about and shes like who?. then i tell her my cousin i think. n then she says mmmm i have a boyfriend. n i im like ok cus i was gonna give it to me cousin but since it wasnt him then i guess it wasnt. then i left. i dont get what i did wrong? the signals were there, werent they? im just like wow cus it felt like she led on the whole way n then said she had a bf and im like wtf in my head lol. i dont get it. can someone please explain what happened or what i did wrongg???