thats got to be bad genes m8, even if you did not have enough light, it would of at-least tried to stretch toward the light
even if you had the worst soil in the world, it would of got many times bigger than that,before looking bad
im sure that is just bad genes .. at 5 weeks its a sad thing to say, but you need to cut your losses , start more seeds , keep these in the corner until you can bring yourself to part/kill them off