Simply adding campden won't stop it, commecial wine yeasts have been bred to withstand campden. You'll have to use campden AND sorbate to do that, it's called "stabilizing." Problem with that is your cider won't carb up & be fizzy due to the chemicals. I don't use sorbate, it tastes nasty to me, but others say they can't taste it at all, it's really up to you.
I'm wondering if you're in a hurry, or if you just like your cider as it is right now, with the residual sugar? You could just bottle, allow it to carb up & then pasteurize. I've never done this, but there are many who have, here's a whole thread on it:
Hope this info helps. Regards, GF.
EDIT: What is the must temp now? Did you use yeast nutrient/energizer/DAP?