"Everybody misses a penalty so there was never any danger that I wasn't going to take it," he said.
McCormack is now on 10 goals for the season with 9 of those coming in the Championship.
"He's a young boy, he's missed one and he stepped up again today," said boss Dave Jones.
"If he'd have missed this one, we'd have throttled him.
"It shows a lot of character for such a young player and he's still developing."
McCormack admitted that Forest had the better of the game but was happy to come come away with three points.
"I think they had the better of the play and the better of the chances," said the striker.
"But fair play to us, we dug in, we kept a clean sheet away from home, which is fantastic, and obviously we sneaked it in the end.
"We know when we come to places like this, we're going to have graft and sit in and try and hit them on the break.
"So we're not going to play the best football away from home.
"But I think at Ninian Park we're starting to show signs at really getting at teams, getting in their faces and playing the ball round about them, which is what the fans want to see."
Forest boss Colin Calderwood is coming under more pressure after another defeats. Forest are on the bottom of the Championship table with just 6 points.
"It was an unrewarding day but I think we have moved forward in one or two other aspects," he said.
"We hope that Paul Anderson hasn't suffered any recurrence of his injury and hope that fatigue was the reason why we had to take him off.
"And Joe Garner has, I think, already showed, unprepared though he was for match action after so long out through injury, a real knowledge of playing up front.
"The benefits to us and him were there for all to reason.
"It was rewarding in lots of ways but nothing that gives us a point or any great amount of pleasure and is obviously no consolation to losing the game.
"There's a lot of brightness about the future - not if you look at the paper tomorrow morning but look beyond that and I think there's things to be pleased about our progress."