I have a similar problem although not yet bottled
I have a batch which appears to have stopped fermenting tested today & have the same SG reading as two days ago, plan to test again Saturday and if there is no change in SG will commence bottling
The brew is on the tart side so need to sweeten before bottling however I understand that if I use sugar to achieve the required sweetness prior to bottling that this sugar will start the fermentation again in the bottle and carbonate the cider
As I want a sweeter cider than it currently s AND I want it carbonated I need to add sufficient sugar for carbonation in the bottle which I can calculate based on the volume of cider produced however this sugar will not affect the sweetness greatly as it will be consumed by fermentation in the bottle.
Can someone recommend a sweetener that does not ferment or leave a bitter after taste.