I appreciate all the suggestions

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I ended up going with the note, asking for her number - and bummer.. didn't go so well

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The moment I walked in, even before getting to the counter she smiled and said "hey!" from across the shop.
Her co-workers are looking and smiling.
This added to the fuel, although i already had my mind set to do it from the get go.
Anyway she wasn't on the cash register - but she passed me my breakfast, and as i grabbed the sandwich, I slipped the note over to her.. FAIL she thought it was something else and said oh thanks and smiled.
Then she realized what it was and "oh.. im so sorry.. i dont give away my number.. so sorry"
I'm not too sure if I cut her off here.. but as i heard them words I kept my head up, smiled and said "no no, it's OK! Thanks"
I was so lost i was almost certain she would give it! My reading is terrible lol.
Maybe i should have built more rapport before going for it. but then it's so hard with the place being always so busy.
Is there a possible recovery from this? what should my next move be?
Grazie tanto!