Sis, please have your OB check this during your next visit or sooner if you're worried, fundal height can vary for a lot of reasons (baby position, amniotic fluid, how you're carrying), and your doctor needs to see the full picture to know if it's okay for you.
Hindi kami dapat mag-assess based lang sa numbers alone, your OB will measure again, maybe do an ultrasound if needed, so don't stress too much yet, but do mention your concern sa kanila!