[Closed] TREK (Carbon frame) excessive cable rub in only a few weeks - how concerned?

I have a 3 month old Trek EX with the carbon frame. It has been used perhaps 20 to 30 times.
The rear gear cable has rubbed into the carbon and caused a hollow of about 4mm. I had not spotted this till today as it is directly underneath the cable (so the cable fits snugly within the groove it has worn.) This has happened right next to the bracket that holds the cable in place.

I have told (and shown) the lbs that sold the bike, who said it is nothing to be concerned about and gave me some patches that are supposed to stop the problem.

I feel as if I have been fobbed off.
Should I be concerned about this wear?
Has the frame been significantly weakened?

The lbs also stated it doesn’t matter anyway as the frame has a lifetime trek warranty

Any feedback would be welcome.
Thanks

Andy