That yeast is notorious for stalling.
When you added more, was it straight from the tube or did you pitch an active starter?
It will take off again at some point. Try rousing the yeast a bit and warm it up. Keep it as close, to that 78° temp, or higher, as possible. Others may have some ideas to give it a boost.
DO NOT BOTTLE IT! Unless you added a ton of unfermentables, that yeast should take it to 1.006-1.009 even with 100% DME/LME. Bottling will lead to bottle bombs.