2 month of orientation and terrified

I am in my second month of orientation and am starting to question my choice in starting out at a rural hospital. When I took the job I knew that I would be doing ER and OB, but not from the start. I wasn't expecting this right out of school and wanted first to get my feet wet in med/surg. The main focus of my orientation has been in the ER and OB. I feel out of place and scared most of the time. The other nurses at the hospital inform me that they like to throw people into these experiences, but I am not comfortable with that. I have little training in either area and one of the classes that I was suppose to be taking, they were unable to get me into because they waited until the last minute to register me. I try to read up on everything I can, but with such a broad area to cover I am beside myself. I still miss a lot of IV's. We only have 3 RNs on at night and my biggest fear is that I will finish orientation and be alone and something will go wrong and there will be noone to help me. I am having trouble sleeping at night. My anxiety is through the roof. To make matters worse the hospital is understaffed and morale is bad. I have expressed my concerns to my preceptor and boss, but they say it is normal and that I am doing great. But, I can't leave work at work. I am full of shame and self doubt and feel like quiting all the time. I don't even enjoy my days off because all I can think about is what if? Sometimes, I think I should be at a bigger hospital where I could get in a routine. Sometimes I think maybe I am not tough enough for nursing. Most of the time I just want to hide in a closet and cry. What should I do?