helllpppp with vivofit pleaseeeeee

Hello I'm recently new and have bought a vivofit , im really struggling to set the step count on it , it seems to go a lot quicker than it should , today it's saying I've done nearly 12000 steps allready and I know I havnt , My other pedometer would be on about 4000 by this point , so how do I know which Is wrong and which is right ,,, really confused