Well even your LDL number is in the recommended range for heart patients in the UK with atherosclerosis, so I cannot understand why. I would think it's just the fact of the family history. However, what your Doctor has to realise is that ASHD is caused by many possible factors and those include many types of lifestyle. If you are not following in the footsteps of your Father with lifestyle, then there are high chances you will not get the disease. Stress for example could have been a problem with your Father, but maybe you are far more laid back. High blood pressure is another important factor.
I think you did a brilliant move there with the scan, and I don't see any point in taking medication for the sake of it.
It's a bit like me taking cough syrup several times a day just in case I catch a cold.