Well done for contacting your GP. It's helpful to talk things through and they won't judge you, any more than we do, they will have seen it all before and should know where to get help and suport.
I'm not sure about writing to the store, let's see what other people here think.
I don't think they will look for anything else on you. Are you able to shop somewhere else?
In terms of how you feel at the moment, I would try to let it go because if you shop elsewhere and pay for everything this will all go away. But remember how you feel now if you're ever tempted to try the same thing again, you can use this feeling to create something good from this.
HB