Poor you! this is begining to sound like a phobia almost! Is there no one that can go with you for some assurance at all?.
The only worry i have when getting fuel, diesel actually, is how much its going to drain my debit card!
I don't live anywher near a really big city bit it seems to be pretty quiet at around 10 PM onwards i'd be quite willing the tag along with you but the old man may not like that!
Have you considered asking your ex driving instructor to have a couple of hours with you at all untill you get that bit of confidence you need at all?
Those new self service ones are very good just stick your card in enter PIN await the instuction to remove card and strat fueling stick the nozzle in and pull the trigger if its filling up it will stop itself when full just put it back in its holster and put the cap back on the car tank close the flap if it has that, and take a receipt if needed and drive off into the sunset LOL!
The only thing that can go wrong is make certian that you put the right fuel in Petrol from the Petrol pump not diesel and IIRC you might have a job doing that anyway as they are differing sizes!.
Why not try a dry practice run first you may get the odd look or so but who cares!?
Or park up near a petrol station and discretly see what others are doing and I promise you there will come a time when you'll just be concerned by how much it costs and wonder why you didnt find this as easy as it is!!