Your feelings of apprehension are SO normal, and even welcomed! Trust me.
I was an aid/tech in an ER and then precepted in that same ER, and I had the exact same feelings -- "they expect me to know 'nurse things' because I worked here, but I don't!" What is worse are the CNAs I have worked with who then precepted on our unit, but instead of having an ounce of humility or apprehension, acted as if they DID know everything. This is frowned upon.
Being an aid and a nurse are two different ball games entirely, so you CAN'T be expected to know how to be a nurse after you graduate regardless of if you were an aid on that floor for a thousand years. It is just so different. But you know what you will have? You'll have the confidence to adequately care for those patients while learning how to be a new nurse because you are already familiar with the environment and you already know how to meet their most basic needs. This is huge -- being a new nurse in a brand new environment is a double-whammy, and even worse if you have never been an aid before, so be thankful that you have this foundation already.
Secondly, never be afraid to ask questions, no matter who you are, who you used to be, or how long you've been there. Nobody will think less of you, and if they do, they are ill-informed as to what your new role as a nurse means. The only way you learn as a nurse is through asking intelligent questions and listening to the answers, and through time and exposure. That's it. Reading your books may help you memorize medications and lab values, but will be of little practical use once you hit the floor and are suddenly flooded with a thousand concepts that you never encountered while in school -- such as the logistics of being a nurse, rather than what xyz lab values indicate. Patients are so, so complex, and the book-knowledge you obtained from nursing school is only one of the building blocks to becoming a successful nurse.
Don't fret -- we all felt the way you do now, and within a year or two you will be soaring and maybe even precepting new nurses. Keep us posted on your progress! Good luck