There will be many times when a patient or family member asks you a question and you don't know the answer...but it'll be okay, I promise :). The best advice I can give you with that is to simply say, "You know, that's a good question. I'm a student, and I'm not sure about the answer, but I will go find out right now." And go ask your instructor or a nurse on the floor, there's absolutely nothing wrong with doing that, and it's encouraged. Always ask questions. If a nurse is discussing something you don't know, ask them to explain (outside the patient's room, of course). Most of the time they will be more than happy to explain anything. I have encountered nurses that aren't so glad to teach students, but you learn to brush it off and ask someone else. You are there to learn, the nurses, your instructor, and the patients all know that.
As for anatomy...just do the best you can. If you're going into the nursing field I'm assuming anatomy is at least a tiny bit interesting to you. Therefore just use your interest and let it help you. Ask the professor questions, go to them if you're having trouble, join study groups, search online for study materials...utilize everything you can. You will not be able to recall everything, but when you hear the word 'alveoli' you will be able to associate them with the lungs and think to yourself 'Oh yeah, I've heard of that". It will really start to click when you get to other classes.
Don't stress yourself out yet, just be excited! Learning about these things are exciting! If you have anything else you're concerned about I'd be happy to discuss them with you :)