Stopping Fermentation

I started a Cider a few weeks ago with an ale yeast and let it ferment out to 1.02 and then cold crashed it. A few days ago I racked it, added potassium sorbate and back sweetened it with apple juice. I needed my fridge for a beer I had just kegged so I took it out and let it get up to room temperature. I just checked on it and I can see that it is still bubbling a little bit and some gas is escaping from the airlock.

What did I do wrong, and how can I stop the fermentation at this point? I have campden tablets, but wasn't sure if I wanted or should add that.

Any help would be appreciated.

It could just be releasing dissolved CO2 since it is warming up. Have you checked it with a hydrometer to confirm fermentation is occuring?

Cold crashing doesnt kill the yeast, it just makes them sleepy and take a nap. If you read the yeast washing thread you will see that people take their yeast, "wash" it, store it in the fridge, then reuse it another day in the future.