Nice buck! I've got one on the wall that goes right at 13.5" inside spread.
Unfortunately, inside spread does not score on an Antelope. If you can, find a Pope & yOung or Boone & Crocket score sheet to help with the scoring. There is boxes for the tip to tip and inside spread measurement, but they do not add to the overall score. It will also show how to properly measure your rack.
I'm going to try and upload a score sheet, but don't hold your breath.