Fully vaccinated, 2 masks and a 180° face shield - I think you're okay. :)
Maybe you can get your groceries delivered?
You could ask at the store if it's an air purifier versus just an air conditioner with filters. My guess is, it's probably the usual store ventilation (which is pretty good at bigger and more modern grocery stores). It's too bad you felt so uncomfortable that you left, especially since you have had both vaccinations and time for them to take effect.
I meant to say air purifier not air filter