Worrier - Should I take my puppy back?

I am a 26 year old and me and my boyfriend have just got ourselves a beautiful tiny 8 week puppy. We planned carefully for her arrival and were so excited, we love her very much. But ever since her arrival I have been terrified that she is not happy, that we made a mistake, that I cannot give her everything she needs, that she might get sick or something will happen to her. We live in a spacious apartment but it is 3rd floor, we leave her in her crate with toys and bed and stagger our lunches so that we can look after her as much as possible. I'm scared that i have taken on too much and i am really depressed, crying all the time, not eating or sleeping from worry. I love her but I feel like Im maybe not cut out for taking care of her and it is having an effect on my health! I cannot bear to hear her cry when we leave, I am in tears till I get home again. Please help, is this normal?? Should I take her back, to be with someone who can take better care?