Is having a larger clitoris a disease?

No it isn't: There is great variability in size of clitoris as there is with penis size in men. There are some medical conditions where clitoris is abnormal as in congenital adrenal hyperplasia. It is possible for clitoris to enlarge if a woman develops an ovarian or an adrenal tum or which secretes androgenic hormone (similar to testosterone). But an enlarged clitoris, by itself, is not a disease.