For the future:
When you receive an Inquiry you can Pre-Approve or Decline. This has no adverse affects on you or your listing as a potential guest may Inquire several listings at one time.
Now when you receive a Reservation request your option is to Accept or Decline. It's confusing because they both have the Decline option. Now declining a reservation request doesn't affect you unless you do this a lot. Then you may see your listing moving many pages back when searching in your area.
If you find that you are declining either Inquiries or Reservation requests frequently you probably need to tweak your listing, length of stays, pricing - something. Because if your listing and everything else is clear you should be able to accept most requests unless you just have a bad feeling about a potential guest or you feel your place really isn't a fit.
But it sounds like you cancelled a reservation that you already accepted. In this case there are penalties - no Superhost eligibility until 2017, you'll move back in the listings page, if done again within the year there are financial penalties and as you see you are unable to book those cancelled days to anyone else.
If the cancellation was in error do contact Airbnb right away so they can help you retain the reservation and avoid the penalties.
Good luck!