okkkk.... well the only thing i can think of is youll have to delete any copies (or move to a totally separate file than where the game gets downloaded into) and download it again from the game page
if it is the demo, then youre just opening an old file or your computer wont replace it when you download it
a good way to check if its the demo is you can download it after doing the above, extract it and then open it up and play it until you get to the next part of the city with the opening credits and see if this character is there. his sprite isnt in the demo at all so if its there then you have the full game and you can play it normally.-
is the only way you know its the demo via the date btw? like you didnt play it and see?