How do I manage a whole project when it overwhelms me?

You can do your own piece well, but managing the whole engagement overwhelms you, the sudden weight of every part, every person, and every deadline resting on you at once. That leap from doing the work to running the work is a real one, and feeling swamped at first is normal, not a failure. Managing is a different job than doing, and it has a different skill: not holding everything in your head, but breaking the whole into parts, tracking them, and trusting others with pieces. You are overwhelmed partly because you are still trying to personally carry what should be shared and organized. The load is real, but it is meant to be distributed. Start by getting the whole thing out of your head and onto one page: the main pieces, who owns each, and what is due when. Look at that instead of the swirling everything. Then handle one piece at a time. Managing feels impossible while it lives as a blur in your mind. On paper, broken down and shared out, it becomes a series of ordinary tasks you can actually do.