Repairing Crack in Concrete Deck Pier

I set this pier a couple weeks ago for a deck extension. I noticed this hairline crack wrapping 3/4 around the pier about a foot from the top. The crack starts from the string I left inside to keep the rebar straight, so maybe that was the cause? First time pouring so lesson learned I guess.

Wondering if I should patch with mortar or use an epoxy like below. The crack is only 1/8th at the largest point...

Repairing Crack in Concrete Deck Pier