Why is aluminium in group 3 of the periodic table?

Aluminum has an atomic number 13

electronic configuration= 2,8,3

we know
period number signifies the number of orbits in an atom.

aluminum has 3 orbits
therefore AL is in period 3

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.