I know exactly how you feel. I reacted the same way when I found out during a CT for calcium scoring. In the 2 .5 years since I've learned to calm down, in part because I go for a CT with contrast dye and echocardiogram every 6 months. I found a good cardiac surgeon recommended by my primary care Dr. who is up to date on the most recent recommendations.
There is a huge difference between having an ascending aortic aneurysm and having a dissection. With 3 scans behind me I now know that for me there is no evidence of dissection and that has remained stable, the aneurysm is stable and may very well have been there my whole adult life. That gives me peace of mind and I no longer wake up every day worrying that I'm going to have a blow-out of my aorta. I did get a medical alert bracelet so that should something happen medical personnel will know to first check for a dissection.

I learned the most important thing is to make sure my BP is managed and to stay active and heart healthy. Educating yourself is the best way to get peace of mind.
I've had to change my exercise routine and medication as well as learn to ask for help when lifting heavy objects. That has taken some effort on my part. No traditional weight training at the gym - now it is lighter weight and more reps. We added a Beta blocker to my existing BP medication to lower the pressure and flow of blood through my aorta. I use Pilates/yoga breathing any time I lift anything, even a bag of groceries. No more using my body as a pack mule to haul stuff around.
Hope that gives you some ideas for taking control and feeling less helpless in the face of a unexpected diagnosis. Just remember, your chances of survival just jumped immensely by knowing you have an aneurysm.