@ Omar
Do you know her well? Do you know her at all? Get to know her, talk to her frequently and be-friend her. If you already know her quite well, ask her out or even just go for a walk with her after she's finished her shift. Take it slow, and don't jump at the fact that she likes you, but rather play it cool. I mean do you like her? If so then 'go' for it
You have something to gain, but nothing to loose.. (in a matter of speaking)
lol
If you dont go to that place oftern then get her number.
What should you have done? Nothing
Just played it cool and talked to her when she came over, ask her some questions.. but dont use a pick up line lol
Anyways gd luck
Edit: oo.. almost forgot, smile at her when she looks at you.. it never fails