I can't really tell from the picture if the shoe is leather inside and out (the fancy surface texture is making me

unsure..)... if it is leather.. have you considered having the shoe stretched at a shoe-repair shop ? that might give you an added 0,5 in size.
Another thing..might the left shoe have been displayed in the store..and the many try-ons made it looser? It seems strange that one should be bigger than the other.
Best of Luck