The Terrors boss also conceded that his players looked nervous during the game, but insisted that the return of centre-back Gavin Gunning will steady the ship.
"We were a bit sloppy and there were a lot of nerves out there. Our defence is maybe not quite there yet but Gavin Gunning is coming back in," BBC Sport quotes him as saying.
"I'll get the boys back in on Monday; it's disappointing but the boys have to be brave: especially at home."
The result moves Cally to the top of the Scottish Premier League after two games played, while Dundee United drop to sixth.