Being a beginner with no real results, my advice shouldn't carry too much weight. I'll give you my thoughts, and you decide what they are worth.
Getting rid of your pattern blindness should be a higher priority than bagging this one woman, though it should be possible to get both. I have no idea how you'd fix the blindness though. I have been subject to it myself, in the past
When you enter the store, try to strike up a conversation for 2 minutes, keeping it flirty, playful and negging her. Then you "have to" go get whatever you need to get in the store, but get her number/E-mail before you go. Let her know you will be in touch "soon" (next 1-2 days) so you can get together for cofee and cookies to get to know each other better. If she is already as interrested as you think she is, it shouldn't be hard. I can't comment on whether 2-3 weeks is enough for her to have gone "stale" though (not enough experience).
Hope it works out. I am interrested in hearing what you do and how it turns out.