Extremely small bump on my phone - when should I freak out ?

Hi, I would appreciate your answers.

After the update I switched to a custom ROM and limited my battery charge to 80% for extra safety, just in case. My battery is good again, even better than before the update.

My phone is a refurbished one (BackMarket in France). I don't know if it's a useful fact. I bought it last year. When you buy a refurbished phone on that website, it says that the battery is already on 85%, it's not good as new. So maybe my battery is not affected by the update, but my phone updated either way.

Well, I've seen some comments mentioning their phone bulging on the back, near the G logo. I checked mine for a long time searching for that bump and after some minutes I felt a tiny, almost flat bump on that spot, in a circle shape, the size of a ladybug lenghtwise. I don't know if the bump was there before, or not.

I've also seen those comments about fires and explosions and, as I have severe anxiety, it obviously made me freak tf out.

My phone doesn't move from side to side when I lay it flat, I can still put my phone case on it with no problem, the back of my phone doesn't open. Just that tiny bump that drives me crazy.

Please, should I freak out and immediately try to replace my battery ? Or can I afford to wait a little and check every day to see if the bump gets larger ? I thought phone explosions were rare. Is this fearmongering or a real concern ?

Thank you. I know it sounds ridiculous but since that awful email I'm so anxious about my phone, about money in general. Have a nice day everyone :-)

EDIT : I'm going to the store to change the battery tomorrow. Even if it probably won't blow up in my face, it's not worth it to be anxious like that. Thank you for not judging me