If you remove the intank fuel pump and it looks like the picture below... you have failed to unscrew the pump and have taken out the nut that holds the pump in the tank as well. This is not good. The fuel is kept inside the tank by a seal that mates the flap surface on the nut. I'm unsure if you can replace this seal. But if it is not in a good shape the tank will leak. You can consider to glue the nut part in place again in the tank using JBweld or any other glue that is fuel resistant. If you fail you end up buying a new tank.