I'd give it a couple weeks before doing anything rash. You just diluted the ABV to 2/3 of what it was before, so the yeast may well jump back to life and start fermenting the cider you've just added. If that happens, you'll end up with a lower gravity and lose a bit of sweetness, which is great if you're concerned about it being too sweet.
More than anything, don't get discouraged. You're going to end up with something good, and the more that goes outside of plan along the way, the better a story you end up with. If you just wanted a bottle of hard cider, you could have gone to the store!