As
BernardSmith said, more yeast will not affect the batch. I suspect that since you only added 3 lbs of berries per gallon then the ph might not be your problem. Most of us here that make blueberry wine use 6 to 8 lbs of blueberries per gallon. I would warm the batch up to about 75°. This can be done by either moving it to a warmer area or by wrapping it in a seed starter heating pad. I say a seed starter heating pad because you can adjust the temperature of it.
I would try another yeast starter as
@BernardSmith described. Also did you add any yeast nutrients to the must?
I would also get yourself a ph meter in the mean time. It is a valuable tool for the wine maker.