I don't fully support the idea that the system is wrong its more the personnel and more so the tactics.
Playing 5 at the back can work as long as the wing backs understand their roles (clearly NG & Bagan do not) and you have some pace in the centre back 3.
With this in mind, here goes:-
Smithies
Sang NG Flint McGuiness Ralls (he's played left back before and been o.k)
Pack Bacuna
Colwill Moore Giles