I don't want to say medication errors aren't a big deal, because they are; med errors can potentially kill someone. But they happen because nurses are human, and I have yet to meet a nurse that has never made a med error. In your four years of nursing, you've never made an error that you know of
If this was even considered a med error for you (shame on the other nurse for not performing their safety checks), as long as there was no harm done to the patient, the error will be written up, you'll explain what you learned, and you will likely never make that mistake again. If there was harm done to the patient there may be further consequences, but maybe not. Owning up to your mistake and showing that you've learned from it goes a long way. Trying to cover your mistakes is what will get you into a lot of trouble.
Don't beat yourself up over it. Errors happen. I know that's easier said than done, because I feel like a total idiot when I make one (2 in 7 years - that I know of - not bad!) and spend a day or two wondering if I'm a bad nurse. I'm pretty sure I'm not, and one med error doesn't make you a bad nurse either. When you get to 25 egregious errors in a short period of time, you can start thinking you're a bad nurse