The correct order of atomic radii in group 13 elements is

On moving down the group, the atomic radii increases. How ever due to poor shielding of nuclear charge by 3d electrons, (135pm)rGa​​<(143pm)rAl​​ Ga has 10 d electrons which do not screen the nuclear charge in an effective manner. The electrons in the outermost shell of Ga experience more force of attraction towards nucleus than Al which decreases atomic radius.