I love - all puns intended - how men assume attraction from a simple pleasant encounter in a coffee shop or checkout. No, she is not attracted to you.
She is busy and trying to get stuff through that till accurately and rapidly. And politely. Just because she is professional and polite - which is her job - does not signal attraction.
She probably thought either 1) you were a needy nuisance - after all, you took up extra time, with your request, or demand, that someone fetch your baked beans - you took up more time and attention and resources than other customers - and required special service - or,
2) that you were a condescending, entitled prat. There are many ways of saying thank you, some of which come across as genuinely grateful ad respectful, and there are others which come across as entitled, patronising and condescending.
Either way, she probably wished you on your way and away from her till as fast as possible.
And, by the way, why not excise 'lovely' from your vocabulary in such circumstances and express yourself more precisely? What is wrong with 'great'? Then, there can be no misunderstanding about misdirected romantic thoughts.