Taking 600mg of vit b12 a day and lab report shows that my b12 level is high (1250pg/ml) than normal (946pg/ml). b12 is water soluble so y was it high?

B12 can be stored: You are correct that B12 is water-soluble and most water=soluble vitamins can not be stored and thus must be ingested daily, but B12 is stored in the liver. While high B12 can be a sign of certain illnesses in someone who is not supplementing with it, it is not unusual to be high in those who take it and not a problem, as there is no known toxicity from taking B12.