The only people that will look at your high school grades are:

The USAF academy--with a D avg, don't even bother applying.

The college that you are going to go to.  You need a 4 year degree to become an officer in the Air Force.  With a D avg, you may have to do some sort of Community college in order to be accepted into a 4 year instituition.  I'm not sure what year you are so you may still be able to make up for lost time. 

Since the USAFA is out for you there are two options for you. 

1.  ROTC-Only offered at certain universities.  Some if not all have cross town type understanding where you can attend ROTC classes while attending your CC.

2.  OTS - Sometimes tough to get into.  You basically get your degree and then aplly for a pilot slot through OTS. 

Google both OTS (Officer Training School) and AFROTC for more understanding.

Hope this helps.  Focus on your dream one step at a time while keeping your end goal in your mind.  Hit the books.