Explain why Scandium is not considered a true transition metal.

By definition, to be a transition metal, is a d block metal, which forms at least one stable ion, with a partially filled 3d shell.
Scandium has one stable ion, Sc³⁺, which posses no 3d orbitals, as Scandium has the electron configuration [Ar] 3d¹ 4s², therefore in its 3+ oxidation state, scandium possesses no 3d electrons.