gas filter leak

i have a 2003 crown vic and just recently noticed a leak in the gas filter area. upon jacking it up and removing the filter i noticed that one of the o rings were damaged . purchased new o ring and that is when the problem started 1st how do i get the ring into the fitting i have been at it for 3 hrs, and can almost get it in and it just folds up and slides on back 2nd it appears that the inside diameter of the fuel fitting is slightly larger on the inlet side i need help sam

i have a 2003 crown vic and just recently noticed a leak in the gas filter area. upon jacking it up and removing the filter i noticed that one of the o rings were damaged . purchased new o ring and that is when the problem started 1st how do i get the ring into the fitting i have been at it for 3 hrs, and can almost get it in and it just folds up and slides on back 2nd it appears that the inside diameter of the fuel fitting is slightly larger on the inlet side i need help sam
Try putting the o-ring on the fuel line against the flange.