What is the risk of me dissecting at a 46mm aortic root and bav? Ascending is at 3.7. My cardiologist and 2 others say its very, very low, negligible!

Stay calm. Malteser, you really need to try to move on. You already know that your risk is very low. Let's put things in perspective: your risk of dying is likely much higher driving to work each day. Your risk of dying in a terrorist attack is very low: do you worry about it each day? How about nuclear war? We all live with risk every day. We make our lives miserable focusing on risks - smell the roses!
Low risk. The risk of aortic root dissection/rupture in the setting of bicuspid aortic valve is not nearly as high as in other conditions in which the root progressively dilates. Most of our guidelines for when to intervene are based on data derived from marfan's syndrome- a connective tissue disease with very different risks. For marfan's we generally use 5 cm as an absolute cut-off to recommend surgey.