When I had my eldest I was terrified of leaving him in the car to pay for petrol.
Luckily, in the village where I lived, we had an Old Fashioned petrol station where a man would come out, fill up the tank for you!, then take your money. Before DS1 I had found this quite embarrassing but after his birth I virtually never got petrol anywhere else.
When we moved 40 mins drive away the thought did cross my mind to go back there for my petrol each time .
When DD was born, DS1 was 18 months and not yet walking. And I had had a c-section. There was NO way I could carry both of them into the petrol station. Pay at Pump stations had just come out but were in their infancy and the only time I tried one it didn't work (NB, OP, Tescos have them), I just had to leave them and sweat it out, peering out through the glass as I waited to pay. Needless to say they were always fine.
So gradually I got over it. Now I have DS2 (14 m) I am going through it all again.
OP, as others have said, you have one baby of seven months old. At the moment you are enjoying the luxury of being able to indulge your perfectly normal maternal anxiety. When you have another child you will probably find that, like the rest of us, you will no longer be able to. And, as someone else said, you will look back on this thread with a little cringe.