2-3 months after a FUE, I began using a Boar Bristle Brush to help absorption of topicals. Did I mess up?

It is best to contact your doctor about post operative care and instructions since each doctor has a different regimen.  Combing your hair should not have an effect on your surgical results.

The result of a hair transplant operation gets complete after a year, this is why we do not suggest any topicals between 6 months and 1 year.

After the 4th day your new grafts are set in their new location.  Using a brush in the 2nd - 3rd month should not disturb the new hair.  Keep in mind that your growth after FUE is not considered complete until you reach the 12 month mark.....you still have a way to go.  If you are concerned, you might want to contact your hair transplant surgeon for his recommendations.