Turn the dread into a list
When the feeling that you do not belong arrives, do not argue with it and do not obey it. Ask it what it knows.
The vague dread is useless. A specific list is not. Write down exactly what you think you are missing, stated so precisely that it becomes a thing you could learn rather than a thing you are.
Then make three moves. Name the gap. Ask the person best placed to see it to describe it, as a student and not a defendant. Study the people who have what you lack: not their results, which are visible and useless, but their method, which is hidden and everything.