If the time it takes for the star to orbit is between 7 and 8 hours, then it's not.
Have you tried changing the time step (in the upper left corner of the screen)? By turning it down, you'll slow the simulation down, so it can be made more accurately. The time step says how long time there is between each time it calculates the position of everything in the simulation, so if it's 1 hour and it takes 8 hours for the star to orbit, you'll get an octogonal shape instead of a circle. If you set it to half an hour, you'll get 16 corners, etc.