I think you are a great nurse. You own up to your mistakes, learn from them, don't make excuses.
Honestly I don't understand about the lab value issue ?????? you did tell someone, that "error" seems kind of petty to me.
Take a deep breath, think Brownbook, an acute care nurse of 30 plus years, is proud of me!
. Laughter is the best medicine to stop anxiety...whatever jokes, humor, you can think of.
I think your instructors are extra harsh, but they have to be, being a student is when you learn.
Three errors in three semesters isn't that bad. You will make more throughout your nursing career. At least you know what to do when you make them. Joke with fellow nurses and students, "I'm an expert on what to do when you make a med error, I know exactly what to do".
I'm positive fellow students have made errors. Either the instructors don't discuss it, or the student didn't get caught and even worse didn't fess up.