That's not unbalanced. School's don't care if someone got an 11. They would care if your score was something like a 15-6-15. That kind score would be "unbalanced". In other words, if you have a bad sub score in any section, THEN it's "unbalanced".
IMO that's OK, tough not well balance....I think if you got 12 8 13 that a little unbalanced...12 7 13... definitely unbalanced. It's not the difference among the subscores, it's how low is one of the subscores. In other words...15 10 15 is not unbalanced but 12 7 12 is definitely unbalanced.
I got a 9/12/12 and asked in the forums if my score was too unbalanced with that 9. Catalyst and a few others responded not to even worry about it since few schools will screen you based on a subscore of 9. I think the only time you need to worry too much is if you get a 8 maybe and 7 definitely or if your overall composite score is not strong