I cry when i get home….I am so unhappy with my new nursing job

Being on Orientation as a new nurse is tough. I see everyone around me and they all look so peaceful and happy. Everyone knows whats going on…except me. Sometimes i think that working in a neonatal ICU as a new grad just isnt for me. Nursing school was’nt this hard.
My nurse manager called me into a meeting and in so many words jsut told me that i have 2 weeks to take on a full heavy load of patients by myself and that if i am not able to handle it that i will have to maybe leave or be fired. This all started when i began having problems with my preceptor and had her changed. Now im in meeting every week to see how i am doing. i hate being under the spot light and no matter how hard i try its never enough. I am fast enough (although all the nurses around me are doing the same tings at the same time) i am not good enough.
I just dont know what to do anymore, i feel like quitting so bad. I really think that i am going to meet with my nurse manager and tell her that this isnt working out for me and that maybe i should be transfered. needless to say i have only been there less then 2 months, 3 days a week. 12 hours a day.