Hi jindi, well there are people who only take 40mg a day, and you take 80mg, so your doc must think you need to take this amount. I take 80mg propranolol a day too, but mine is in a slow release pill that i only take in the mornings.
It can be that there are peaks and dips taking them as seperate doses, and probably because they block the adrenaline from reaching your heart, they can make you feel quite relaxed, so yes it could be that one dose wears off before you take the next, so you could be feeling your anxiety inbetween doses.
Cathy