Okay, I'm guessing from your prior post that CSU refers to a California school (as opposed to Colorado or ???), and that the fee waiver you're asking about is an application fee waiver?
If you misstated your income in order to get a benefit from the school, you should correct that ASAP. No one will hold it against you if you say you made a mistake, so long as you correct it. But knowing you made a mistake and not correcting it is fraud . . . which is a lot more serious.