I would assume the majority of your Nursing pre-req courses will overlap with your Biology courses so you should be on track to finish that Biology degree even if Nursing school is not in your future.
Here is the link to the Nursing course curriculum and seems to match pretty closely to a Biology major course plan:
http://www.nursing.uci.edu/bs-prospective-students.asp
UCI’s Biology 4 year curriculum: http://catalogue.uci.edu/schoolofbiologicalsciences/#bioscimajor