summats not right

The AF point was on the word with the pen marks around it but clearly the in focus area of the image is some way in front of that point. Its OK at the long end, but wide is where I am getting this fault.

Its a cheapo Tamron 70-300 but only 6 months old - back to shop where I bought it or for repair/replacement or will they simply say 'thats as good as it gets for a cheap lens?'