No, your state's (CA) law plainly states that if you report to work and are an hourly employee, you must be paid at for at least half your scheduled shift, up to a maximum of 4 hours (if it had been an 8 hour shift; for a 6 hour shift, you'd have to be paid 3 hours, etc.). Because the law requires this, you cannot "volunteer" to not get it; employees cannot volunteer to get less than the law requires they get, which is why an employee cannot "volunteer" to work for less than minimum wage, or a non-exempt employee volunteer to not receive overtime. They must pay you for half your shift.