The fitbit isn't designed to tell you just what you burn when you exercise. This is what you burn with just normal living day to day. Depending what time it was when you set it up, you may have done it later in the evening. So it is telling you on average what you burned just breathing and living through the day.
as you exercise, the calories burned will go up on the website. it takes your peaks of high movement and determines that is when you are working out so you will see a bar graph toward the bottom of the fitbit page. My fitbit report has two spikes-- One around 12:00 when i take a walk or do stairs at work and another when I do my higher intensity exercising.
I have found that what Fitbit tells me to do and SP are very similar.
| current weight: 250.0