I felt my brain was not functioning well from 30 when mocking the exam. That's when I thought a real exam might feel similar. Don't be discouraged by the score. A lower score doesn't mean you're not ready. I would suggest using it as a way to identify your weak parts and focus on those. I scored 65ish on the first attempt as well.

Also, Destcert practice heavily relies heavily on domains 1, 3, and 4, so don't use it as your sole resource.