Dear student,
Since boron has to form the bond with three fluorine atoms in boron triflouride (BF3), so, it involves two atomic orbitals which are s and p orbitals in boron outermost shell. These atomic orbitals mix to form three equivalent sp2 hybrid orbitals.These orbitals are called sp2 hybrids which means that this set of orbitals is derived from one s orbitals and two p orbitals of the free atom.
Regards