3 yr old with autism

my 3 year old son has been diagnosed with ASD,but i dont think he has it i just think he is a very shy boy and just behind for his age.could they of diagnosed him wrong?they only saw him for an hour so they dont know him like i do.i am very shy myself and can also be un sociable as well so may be he just took after me.has any one eles child been diagnosed but they have got it wrong?