Aufbau says that the sublevels fill 1s2, 2s2, 2p6. That would mean that you must have filled 1 and 2 s (=4) and 3 more.
Last I checked, 3 + 4 = 7. Which element has 7 electrons?
I'll give you a hint: its atomic number is 7. Another hint: its symbol is N.
