You don't have popcorn lung.
However, if you are worried about it, go see a doctor.
Also stop using your friend's Juul. If it's causing you THIS MUCH angst, there is a very simple solution. Stop using your friend's Juul and don't buy any more vape equipment or vape ever again.
If you have even a HINT of the slow, deadly and totally imaginary case of Vape popcorn lung, I believe you have a chance at a totally normal life, if you cease vaping.
Uh, also, if you read about popcorn lung somewhere (I mean you MUST HAVE, right?) I can't imagine why you started vaping in the first place.
If you read about the slow, deadly and totally imaginary case of Vaping popcorn lung by excessive googling after catching a head cold or allergy season started, well, STOP VAPING, and also, do not google late at night and also not after having completed some science and statistics courses, well STOP DOING THAT too.
In all seriousness, my sympathies and all, I know it's scary thinking you have a disease (imaginary or not) and go to the doctor, but I'm 100% certain that you don't have it. Something else maybe but not that.
Anna