First, are you being seen by a thoracic surgeon at a center that does a high volume of ascending aortic aneurysm repairs? If yes, I would meet with that surgeon and ask what factors may have caused the increase - if it truly is an increase. Were measurements done on the same CT or different CT scanners? Was contrast used?
You are looking at millimeter increases. Look at your ruler and see how small that is and how difficult it might be for a reader to be absolutely accurate.
You might also ask to see a vascular specialist and request a PET scan to see if there is any vasculitis in the aortic walls. That will give you some idea about risk. Possibly the treatments that you had are causing the issue - again, if there is an increase.