He's only been with you a few days then? I would let him get used to his new surroundings before I labeled him as fearful or shy. My pup took a couple days to get used to us and our home before he came out of his shell. He was still a little shy, but only needed a little confidence building (through socialization). I would up the socialization (but make sure he's enjoying it, it might be socializing from a further distance at first) but also give him time to adjust. It's hard to say just based on what you said if he's just taking his time getting used to you, or if he is indeed fearful. Either way, with socialization, obedience, etc. you can definitely turn this around - he's so young!
Does he know "come?" They need to be taught to come before they will reliably and in just a few days, I doubt he has that mastered.