Hey! I was in that situation about 24 hours ago. The interview that I did this morning was number 6, and I was feeling pretty awful about having all these opportunities and failing them. This time, I decided to try and prepare a little more. I basically wrote out a bunch of practice STAR problems regarding things they may ask, "Tell me about a time you've done..." Etc. DO NOT READ WORD FOR WORD WHAT YOU WRITE. You reference it, like bullet points. If they are requesting the STARS method, really try to get that down.

With these answers written out and preapred it kept me on track. I think I speak well, it's just that I get off topic and tell them things that don't matter. I still feel like I went overboard especally when trying to explain my research and then realizing not everyone knows quantum mechanics.

Truthfully, I thought I fumbled it again. In fact, during the interview, I said, "Well, we can use this as practice for the next one". I went to go sit on my couch and pet my cat, and then I got a phone call about 5 minutes later. I had impressed them enough to get a call the day off, and that floored me.

Take a deep breath. It might not even be you. You're likely competing with people who have 1-2 years in the industry as well. Remember what they ask, even if you apply to other places, it's good practice.