1. take a gravity, that will tell you if you are done.
2. while you saw some evidence (bubbling) just because it has stopped doesn't mean your fermentor isn't leaking CO2 out some other crack - usually the lid, so it could be still going thus #1 take a gravity.
3. IF after an extended time - at least 7 days - the gravity doesn't get to expected FG+abit then yes you could put in another yeast pitch to bring it down. But first make sure you do #1 and take a reading. And sample, your taste buds will tell you a lot about the quality.
How quick the fermentation is depends on things like amount of yeast pitched, temp of ferment and other factors. So it is possible that it is done, although personally I'd doubt it. Take a gravity and let us know what you get. If you have your OG or your receipe that would be helpful also.