Depending on how you shot it (RAW or JPEG) you could go back and adjust the levels. My first thought though was to use it as a stock sky. If you can go back to the colour version (if it was shot in colour) this could be a really useful sky layer for other landscapes that do not have such an impressive ceiling.
Remember though! If you use stock skies as layers on other shots you have to be very conscious and careful of the light direction.
Hope you can improve or use it to your advantage
