I was in a somewhat similar situation, but different school and more expensive. I had my doubts before I was accepted--but more a fear of debt. My friend said something that resonated with me in regards to my doubts. She said that if you go into it and realize it is not right, you can always change your mind. People do drop out of graduate programs when they discover it was not right for them. At least you will know that it was the wrong choice. However, if you never try it, you may at some point regret it or wonder what things would be like if you had done it.
What will you do at that point? Sure you can change your mind again and reapply, but as you know getting into UCSF as a direct entry student is a challenge in itself.
I am not saying you should just jump into it with doubts--I don't even know you. But, I do think it is normal to have these concerns before making such a big life-changing decision.
Can you think about where you see yourself after you have graduated? And then in another 5 or 10 years? Can you create a different picture without the nursing degree? If this program is going to lead you to your dreams then all of the other stressers and beaurocratic bull$#@! will work itself out.
I think I will just jump in with eyes wide open but know that nothing is permanent. Best of luck in your decision making!