noob question for d600 af points.

i am a new owner of d600. i've been using d90 for years with full frame lenses. please take note i'm just a photog enthusiast. I was testing my d600 af points i noticed that the side points left and right is having a hard time focusing or a worse doesnt focus at all? is that normal? i'm using af-s with single point option. otherwise if this is a problem i will ship it back to amazon and ask for replacement.

thank you in advance..