Good luck to you. Just a suggestion, carry a small notebook, write down diagnosis, labs that you're unsure of and when you get home look them up while they are fresh to you. I think it was the best way to learn. Ask questions, but not in front of patients, it might put your preceptor on the spot. Take a deep breathe, a lot. Welcome to nursing!!!!
You're talking about YOUR career here. No one needs to tell you that it's hard to find jobs period not to mention one that pays like nursing. Take some time to step away from the situation, write her a letter that you never intend on giving just so that you no longer hold onto what you're feeling. You're a nurse,, it's not a job it's a calling! Don't let someone cheat you out of what you're meant to do.
You should try to have your record sealed leagally, If you made a immature mistake and have been a solid person since then. You don't need ANY odds stacked against you as a new nurse. It's already hard for new grads.