First- The whole license thing. Not sure where the myth came from, but it is a persistent them in nursing, and on this site
You will see a lot of fear, but not a lot of first hand experience of losing a license for a medication error. And certainly nothing about people actually being disciplined for something done by somebody "working under my license"- another weird fear/myth.
Go to your state BON, and see why nurses get disciplined. Then, don't do what they did, which for the most part involves working impaired, committing felonies, diverting narcotics, that sort of thing. If at all possible, you should avoid being caught on video abusing patients, which can also cause problems with the BON.
As far as making mistakes and negative outcomes- That really is kind of a thing. Medical errors are a pretty significant
source of patient harm in this country. And, while they are studied, it is highly likely that they are under-reported, and really hard to study. Many errors are known, but not reported for fear of discipline, and many errors are simply unknown. Mr smith and Mr Jones live in adjacent beds in LTC, and were accidentally given each others meds- all 20 of them. Mr Jones becomes lethargic and hypotensive, but nobody will ever know why.
I am guessing your instructors are trying to instill vigilance, rather than fear. Understanding the potential for the harm we, as nurses, can do is a good thing. So, if I am teaching you about epi, I am probably going to make sure you know that a misunderstanding in concentrations can, and has, caused deaths. If it makes you so scared it clouds your judgement, I have done a bad job, On the other hand, if you double check each time, and get another nurse to also check, I have done a good job. A tricky balance.
And, as mentioned, you will make errors. It is even likely that at some point, some harm will come from your error. In an ideal world, some of your early errors will be harmless, and will help shape your nursing practice and improve it. I know my errors have dome that for me. Or at least I hope so.