I would look into pitching some Malolactic Bacteria to address the sourness:
Dry Culture -
Lalvin Bacteria
or
Wet Culture -
White Labs Inc.
Then to address the dryness I would add a similar juice that hasn't been fermented, Welches Concord or whatever you think is similar and/or will complement. Make sure you sterilize and stabilize before adding the juice... or else it might kickstart fermentation again making more dry wine!
If your really concerned about your batch; post a PH Reading, before/after Specific Gravity, and about what your primary and secondary temps are or were!