It gets easier if you stop worrying so much about what these strangers think. Tip 15%, let the receipt checker roll their eyes when you walk past, let them judge you on your self-checkout speed, etc. Who cares?
I.e. costco introduces self checkout, don't use it, then they start putting people to pester you to use it/try to check your card before you get to where you need (because non-members use self checkout), then they introduce door checking of membership.. all of this is over their desire to reduce staff in the store and force self checkout.