Firstly, take a reading. You can't have any idea what to do until you do that. Bubbling is not a good indicator of activity and the yeast can't read a calendar.
If the reading is about where the kit claims it should be wait another week and take another reading. If the two readings are more or less the same then it's time to start deciding if you want to dry hop, if you want to dry hop in presence of yeast or not.
If you decide the beer could use more hop aroma and that fresh dry hop boost then you have to decide if you want to try, for simplicity sake, just dry hopping in the primary. This is the easiest method but the yeast and hops interact and create changes in hop flavor.
don't worry about the headspace in the carboy, if/when you rack the beer over enough co2 will come out of solution to protect the beer.