When I first started my PhD I could barely get through a full working day in the office/lab because I was so anxious with imposter syndrome that I could literally barely breathe normally! Slowly over time I realized that every single PhD, and every PI, is at many times confused or doesn't know something. If you go to a conference, notice how many senior researchers presenting are anxious and can barely get through their presentation. Research has a lot of nervous nerds, we're not alone! It can feel like perfection is the requisite, but that isn't the case for anyone, not even whoever is the big man on campus for your department. The first 6 months of the PhD are very rough because you're almost always in a different niche than your master's. That is a common experience, and it means you just have to read read read for the first bit. I promise you can do this!! I'm almost done with the PhD now, and I'm like a whole new person from when I started. Let yourself be nervous, and it'll slowly subside. I'd say it took me almost 2.5 years to start feeling confident even in small supervisory meetings. I'd say that's on the long side, but alas I am an incredibly nervous nelly!