First I am so very sorry about your father's death. Because he had CC does not mean that you automatically get it. The fact is, many people who get CC have no family history of CC.
Then i want to say that a lot can happen in 20 years. There can be a lot of progress on treatment and diagnosis. You are very aware of things, so you can be very proactive about your health. You can adjust your lifestyle, for example, eating better, exercising more, etc. Unfortunately none of us has a crystal ball. You know, control the things that you can.
I am sure that doesn't make you feel any better because you lost your wonderful father to this disease and life is feeling pretty fragile and unpredicable for you right now.
My best advice is to stay in the moment, enjoy your days, love the people you love, do the things you like to do,...well you get the picture. All things that are hard to do when you are grieving. Take your time, accept how you feel and try not to judge it or yourself too much.
I hope that wonderful memories of your father replace your sadness soon.