Why does it terrify me to be the one who finally does it?

You have assisted a hundred times. You know the motions. But when the task becomes yours alone, your hands change. This is not a skill problem. You already have the skill. What changes is exposure. When you assist, failure belongs to someone else first. When you act alone, failure has your name on it, with nowhere to hide it. That is the actual fear — not the task, the full ownership of its result. But notice what you are forgetting: you are not actually alone. Your team sees you. They will catch what needs catching. The work now is to stop treating 'alone' as a true description of your situation, and start treating it as a story you tell yourself to justify waiting.