The biggest advice that I've heard to keep yourself calm is to treat it like a practice test. That's easier when you have two or three lined up, so there's less pressure on each one. Does this have to be your last test? Is it for admissions cycle timing or are you out of attempts?

Also, I think you'll be fine if your pt score are as high as you want your test score to be. There's variance of course, but if you've done a couple official tests you're probably used to that. I think worry about how to calm yourself down can be unhelpful. We're all a little nervous on test day but you'll be fine. You know how to do the problems.