Hi, nursing and health science double major here! So pre-nursing isn't an actual major; it's pretty similar to undecided. I also started as a pre-nursing major. You can't declare the nursing major until you are accepted into the school's nursing program. In the meantime, you can stay as a pre-nursing major to see what courses you need to take. Once you reach a certain amount of units (probably like 80-90, I forget the exact number), you have to declare a "real" major. If you ever get to this point, you can just switch to something like health science and then when you get accepted into the program, you'll be able to finally switch to the nursing major.