My heart goes out to you because I was exactly in your shoes a year ago and thought I'd picked the wrong career. I really struggled during my preceptorship, and wanted to quit several times. A lot of it was just nerves and fear. Plus I was under the misconception that I had to know everything right out of nursing school, and so was ashamed to ask for help/advice. Big mistake! Why? I finally learned that it's not all about how I looked or what people thought about me, but ultimately about the patient's SAFETY. In fact there are seasoned nurses on my floor who still ask for a second opinion. You might think you look incompetent for asking the charge RN for a second opinion, but actually you are being smart. Better an early intervention now, than having to call a code on a patient later. Trust me you are on the right path, and it will get better. Just stop comparing yourself to others. Measure your progress by how much you are learning everyday and by how much better you are today than you were yesterday, or a week ago.
As to time management, that will come. I still struggle with it, and often have stay on after shift-end to catch up with charting. But I don't mind, because at end of the day the most important thing for me is that my patients are safe, stable and cared for.