Your rating will become more accurate, after you play more games.
Look at the absurd case: Your first game, you beat a 2500 GM (he suffers a disconnection or blunders). Would you expect a rating greater than his?
Of course not, and that's why ratings are based on many games.
Till now in Online Chess, i haven't lost a single game and beat a 1048, a 1318 and a 1601. still my rating is 1559 . how come? since i beat a 1601 with no loss, should'nt my rating be more than his ?