I think even the bravest of us will retain a kernel of that fear, even if it only shows itself in those final moments. Death is a great transition, a step into the great unknowable. You realize that your convictions about what happens after seem relatively insubstantial, based more on personal preference and affected by bias. Your paradigms, convictions, and beliefs will be challenged in ways some may not have been braced to face, and so they pull their punch, or back out before it is too late.
And there is nothing wrong with that. It is far better to go when you are ready. There is a lot of material out there with excellent advice on how to process your eventual death, on how to release the attachments that may be binding you, should you wish to release them, and on how to process that fear and stress and indecision in a healthy way instead of just trying to brute force your way through it.
It can be a bit bracing, confronting our own mortality. Like the initial bracing shock of leaping into a pool of cold water. But if you keep moving through it, and with it, you'll warm up a bit and get more comfortable with the concept. Don't be afraid to give yourself the time and space you need to work through those uncomfortable feelings. Don't suppress them as soon as they crop up - try to sit with them and let them say their piece, show those parts of you love and acceptance. Acknowledge your fears and remind them that everything will be alright, in the end.
Meditation and Buddhist philosophy has really helped me with the process, personally. There are many historical monks that have committed to the long and painful process of self mummification, or immolation, in a state of zen and peace. Perhaps it may be possible to get so close to 100%, the remainder doesn't matter.