The number of atoms in a hcp unit cell is

The number of atoms in the hcp unit cell is 6.
3 atoms are placed in the middle of the unit cell. The contribution of each such atom to the unit cell is 1.
2 atoms are present at two face centers.  The contribution of each such atom to the unit cell is one half.
12 atoms are present at 12 corners. The contribution of each such atom to the unit cell is one-sixth.
Total number of atoms in one unit cell = $\left(3\times 1\right)+\left(2\times \frac{1}{2}\right)+\left(12\times \frac{1}{6}\right)=3+1+2=6$