Because according to the narrator money lent over a bridge table or for drinking soda water does not need to be returned but a kind of loan that he has given to Todd ,that is a dollar must certainly be returned .The narrator has a hypocritical mentality hence he thinks that way.
He won"t return the money because as it is given in the story, if everyone comes to him all at once,  he won't be able to pay it altogether...the author has also written this to add humour to it.
but later in the story he says that if the people come to him one by one he would pay them...
No. The narrator has not mentioned that he WILL pay them back but says that he will write their names down on a paper he does not actually intend on returning them as he is hypocritical..