I can’t imagine you have anything to worry about. You are absolutely allowed passengers, and as you were in the car doing something you wanted to do, that’s to your benefit as it was something you wanted. The car isn’t just there for you to do your shopping and nothing else, it’s for all of your transport needs. Someone else also benefitting WHILE you do shouldn’t matter, otherwise you wouldn’t be able to take kids to school or a whole host of other things.
The issues usually arise when named drivers are using a car in a way which doesn’t benefit the customer directly, not how the main user uses it, other than things like business or delivery/hire which are separately covered by specific exclusions.
Of course, this is all just MY opinion and shouldn’t be taken as absolute fact.
"Man is born in freedom, but he soon becomes a slave, in cages of convention, from the cradle, to the grave."