Well firstly relax and divide the task in small steps. If you have any doubts, take help of your colleagues. Lastly, don’t take tension

Hey. No one starts as a director or a boss of the company. You always start at lower positions where you have a lot of place to learn aka "to make mistakes". The most important thing is to show up at your work and to do the things you re told to do. It is normal that at the beginning you will not make it 100%perfect, but you will learn it in time. It is normal to get anxious: it means you care about the job. The important thing is to make effort. Help yourself in a way that you write down steps you need to do, ask a collegue to help you out or just to make sure that you do the things in a right way. And also think about this: learning proces is long. Probably they would not hire you if they thought you re not right for this position. Good luck!

Is there any reason for you to think that you can't perform

Do you map out or write out task plans? It may help you to understand what needs to be done, and give yourself goals within your work assignments. What makes your most anxious, missing deadlines, quality of work, lack of direction, etc.?