Most of your what ifs are just head games with yourself. Stay alert on your bike, know where others are around you. Keep your bike in top shape with good tires and watch the road and trails for sharp objects like pointy rocks. Don't know how long you have been riding but just keep your mind on you and your road and you will relax a bit about your worries. The one thing I watch out more for is when people are merging into traffic that they don't seem to see bikes and the sign that says YEILD. They think the highway is supposed to slow down for them or they don't speed up to merge.
Have the confidence to know you can avoid most anything by giving yourself room and knowing what is around you.