Fitbit

My Fitbit is often wrong. Today it tells me I took tover 5, 900 steps. Dead wrong. It did not track my bike miles except a very short part of the ride. I follow the directions over and over and still get no bike miles. I want to count calories in and out, but how can I trust the thing if it can't synch or overcounts steps. The bottom of the Activities on line gives me a chance to log my bike miles, &c. But isn't the Fitbit supposed to do that for me?