Feeling really discouraged

So it's my first job out of nursing school and despite the fact that I like most of my co-workers, I really want out of my unit. I have had 2 separate instances with 2 separate preceptors who have given me misinformation on how to do a procedure. The first one resulted in a note on my file, but no write up, and when I talked with my nurse manager, she said that the second instance was just something that I need to do right from now on, since I know better. I try to watch any procedure that the more experienced nurses do because it always helps me to see something a few times to get the hang of it. The procedures aren't something that we do every day so I might get to see it once a month or so. Neither patient was harmed, but I really want to be a good nurse and it just makes me angry at myself for doing it wrong. We have a nurse educator, but not on my shift. I was watching a more experienced nurse access a port the other day and saw her contaminate the sterile field with a pre-filled syringe. It is not just the one nurse either, I have seen a few do it. My question is, how do I keep this from happening again when I don't trust the info I'm getting? It's not like I have time to look up every policy and procedure before I do it. I'm not sure if this a case of "this is how we've always done it" or if they were given misinformation too.