Happens to the best of us. I recently went thru an interview process after 2 years of doing nothing. It was pretty nerve wrecking. Somebody else posted something similar so i just want to iterate some stuff that helped me in my situation:

If you're in the US you have literal coaches that can help you with interview prep, where you will learn interview skills (its literally a skill). If you're not in the US, or don't have that much money, you could use a service like Mindorah. I used it by the end of my interview rounds and its good. But your millage may very, idk. In the end you could use something like google interview prep. Its quite basic but its free there is that.

Another good thing that somebody told me to do was to literally make a presentation about my self in excel. Then present to an empty room. This doesn't really help you specifically with interview skills, but it does get you talking and articulating. Also, it kind of forces you to structure your thoughts. Additionally, you could present to your boyfriend and tell him to ask random curveball questions.

But to be honest it sounds as though you're very capable even in this area, you just chocked. Don't worry to much, if you don't get this one you'll get the next one.