If an atom has the same number of neutrons as protons, it means it is an isotope with a neutral charge. The atomic mass of an element is the sum of the protons and neutrons in the nucleus of an atom. Since the number of protons and neutrons would be the same, the atomic mass would be equal to twice the number of protons or neutrons.
If you added another neutron to an atom, you would have a different isotope of the same element. Isotopes are atoms of the same element that have different numbers of neutrons. The element itself remains the same, but the mass number (sum of protons and neutrons) and other properties may differ depending on the specific isotope.