The B team lost 4-2 to Airdrie but saw Cole McKinnon’s strike appear to cross the line at 3-2 but the goal wasn’t given.
McCallum reckons it should have been given but says his players showed plenty of quality.
He said: “I think you saw some of the best of what the lads can do, especially in the second half, but you also saw what we need to work on defensively and decision making in the goals we lost.
“There is a lot to be pleased about but the boys are clearly disappointed. Decision making can be pivotal in whether you win and lose and that’s frustrating.
“At 3-1 we were excellent. We were relentless in our attacking play as we had been passive at times in the first half.
“We allowed them to dictate but we controlled the game after the break and had an attacking threat.
“Cole hit the bar and it is a debate whether it crossed the line and that’s frustrating for us.
“At that point we could have made it 3-3 and we were the team on the ascendancy, at that point I felt we would keep going.
“We maybe surprised Airdrie with the level we got to but I wasn’t surprised.
“I know what they are capable of but over the game we have players who want to get to the first team and it is building bridges to where they want to be.
“We had good spells individually and we are frustrated but it is a game we feel we could have won.”
Josh Gentles opened the scoring with his second goal in two games with Kieran Dowell also netting.
McCallum was delighted with the 16-year-old’s impact and believes it was another step in his progression.
He added: “He was excellent. He is only 16 and he had boundless energy.
“He showed good quality, he took the ball under pressure against good players, but he stood up to it brilliantly.
“His goal is excellent and he showed good link up play. He can be pleased with his contribution and hopefully that is the next step in his development.”