Unfortunately, there will always be questions you cannot answer. Your gift to your patients is not in knowing everything, but your willingness to share what you do know, and being willing to help them find answers. Patients ask me questions all the time that I cannot answer. Do you know what week the vocal cords develop? I certainly didn't. I responded, "I'm not sure, but I will look it up for you".
Your fears are very common due to the sheer amount of information to learn as a new nurse. You will never know all the answers during your career, and I find that patients (and co-workers, for that matter) will respect your humility more than a genius intellect. You have a lot to offer and I wish you the best of luck in your career.