I work in a shoe department, and shoes can only be returned if unworn, or if there is a visible fault with them. Blisters and discomfort are related to shoe fitting problems and cannot be classed as a fault, unfortunately.
However, I do know where you are coming from with Converse - I have some and have only worn them about twice as they kill my feet!
The only thing you could do is go back to the shop and see what they say, you've got nothing to lose by doing that. Alternatively, try wearing thicker socks or plasters as padding for sore spots.