The first results are always fun I wonder what EI you used on the film? The contacts do look rather underexposed, as you say.
D76 is pretty much the same as ID11 (the Ilford version of the same developer type) and for that developer the 13m time is for an EI of 6400. To get attractive results at that rating you might be better using one of the Ilford recommended developers - either DDX (a liquid concentrate) or Microphen (mixed to a stock solution from a powder) which are both 'speed-increasing', in comparison to D76/ID11. Even then, try rating at EI3200 and using the development time for 6400.
The films actual ISO speed is around 1200 but it is designed to have a very flat curve, allowing over-development to increase contrast and give a 'normal' looking result at higher EI's (in other words, it is made to be pushed). A lot will depend on exactly how you meter the scene as variations can easily give you a stop more, or less, of light going on to the film. For portrait work this might not be a conventional choice of film, to say the least.