The LM732 is just a linear regulator, which can't boost the voltage. The maximum output voltage is always a few volts less than the input voltage, so you'll be lucky to get anything greater than 9V, with 12V in.
To get a higher output voltage, than the input voltage, you need a switched mode power supply. In your case, there will be occasions where the output voltage is less, as well as greater than the input voltage, you need a topology which supports that such as buck-boost, SEPIC etc.