It sounds like you are doing ok so far, maybe your just feeling a little overwhelmed with the change at the moment. I remember when we adopted our dogs i had a bit of confidence wibble right before they came home and a few days after. Even now i have the odd day that i feel like i'm a rubbish owner which isn't really true, more a case of low-self esteem. Depression can give you a warped view of things and make you not very kind to yourself. You might find this MoodGYM site useful

Can some friends/family help you with your new pup and reassure you? However if your really finding things too much then there's no shame in returning the puppy.