How worrying is damage to a carbon fiber frame near the bottom bracket?
I would be concerned. The bottom bracket is the most heavily stressed part of any bike, and carbon has a catastrophic failure mode--that is, you don't get any warning. One minute it seems fine, the next minute, you've got carbon-fiber shrapnel.

As a first measure, I might clean it up as best as I can, take some pictures, and send them to the manufacturer or the manufacturer's area rep to get their feedback.