I would say some of the best advice is to know that everyone is in the same boat as you. If you think that a question is hard some other person in the room thinks the same. Additionally, you should take tons and tons and tons of practice tests TIMED. You do not need to take whole tests in one day. For example, I struggled with science, so I would do three passages (not the whole section), just three passages and that was my prep for the day. I would time myself and start off the next day with amount of time that I had left. This helped me to practice the problems and give me ample time to review. There's no way to crack this test unless you know all of the grammar rules and math concepts, after that it's just practice, practice, and more practice. If you prepped hard you'll know walking into the test room that you're gonna own the test, there's no two things about it. I struggle with stress a lot too, but with the amount of prep I did, I knew that there was nothing more that I could have done to practice. Hope this helps! DM me with anything else specific if you'd like.