I work in the ER and understand where you are coming from. Don't expect to do everything yourself and you need to get that "being perfect" or trying to be a hero mentality out of your head. If feeling overwhelmed which happens to even seasoned nurses in the ER, just ask for help or let your charge nurse know. No one will look down on you and being a new grad fresh off orientation, your coworkers will perfectly understand. Don't beat yourself up, you are still learning.
ER can get real crazy and chaotic in just minutes and you need to just roll with it and rely on your coworkers. Hang in there, keep a positive attitude, continue learning, ask questions, and be a team player.