First interview in 20 weeks - 20 weeks in

After 16 applications I finally got a call for an interview as an accounts payable clerk. This is my first time dealing with any of this. I tailored my résumé and added a short note. How do you stay calm?

Thanks for writing this out. I went through something close to it 8 months ago, and it settled down once I kept a simple log of every call and form.