Hi Pam,
looks like it is not possible currently to adjust font and size in columns headings, in reports.
You can have a look to this thread:
https://community.apptio.com/communities/community-home/digestviewer/viewthread?GroupId=1531&MID=24880&CommunityKey=c7d27b12-3c91-4da1-a359-3fbf51914009&tab=digestviewer
You will see a solution for improving font in column values, but not for Headings.
Hope this can be of some help
#CostingStandard(CT-Foundation)