Hi!
Go to Terminal 2 , there's a cinema and other things to do there. Basically like a shopping mall. If you want to do some proper shopping then you could get the MTR to Tsing Yi where CityGate outlets is. It's not that far and you could make it there and back within the 4 hours.
What ever you decide, have fun. I go every year to HK to visit my grandmother and I still haven't run out of things to do there!
