My stool has a groove in it, almost like someone scraped a line with a toothpick. Should I be concerned?

No . I don't think you should be concerned. However, if you notice that the stool caliber is becoming thinner or if you see blood in the stool/from the rectum or if you have new change in your bowel movement/ worsening constipation, weight loss etc in addition to the above-especially if you have positive family history of cancer- you should see and discuss with your doctor as soon as possible.
Unanswerable. I have watched this question not get an answer now for a few days. I believe that it is such an odd or unusual question or situation that medicine may have nothing to offer. And, that alone would be likely to mean there is nothing to be concerned about.