In the club's sole match during their six-day stay up in Scotland, McCall's men lost out 2-0 to the Scottish Premier League side thanks to two headed goals from set-pieces within five first half minutes.
Despite the final score, City saw a lot of the ball, dominating the second half in particular as they looked for a way back into the match.
McCall said: "You never like losing any game but if this was a league match we'd be devastated at losing it given the balance of play.
"We've conceded cheaply twice from two balls into our box - that is clearly unacceptable - but some of the movement and some of the play from the lads was excellent.
"There were a lot of good performances from us out there but we know we have to work the 'keeper better after having the amount of possession that we had.
"Conceding two set-piece goals like that will have also shown the players that we can't accept that once we come round to playing for points.
"We had to change one or two things around defensively with young Danny Devine coming in at left back but the lads know we will tighten up on that.
"There is always things you can work on but a lot of the lads got 90 minutes under their belts so there are a lot of positives to take from the night.
"We will continue to add to the squad but we've seen tonight (Tuesday) that we already have good footballers in this team."
After featuring for the club for the first time in the second half at Gateshead on Saturday, recent loan signing Jordy Hiwula played the full game for the Bantams at McDiarmid Park.
McCall continued: "He looked lively, particularly in the second half.
"He showed good energy and good pace, and he'll get better the more game-time he gets.
"The plan originally was to only play him until about seventy minutes but we gave him the full game partly due to a couple of knocks in the squad limiting our other options.
"He says he felt fine after the game and he looked to be enjoying himself.
"Getting the first full game under his belt will help him fitness-wise."
The three James' of Hanson, Meredith and King all missed out on Tuesday evening due to recent minor training ground knocks, while Joe Cracknell and Reece Webb-Foster were also carrying small injuries.
McCall added: "James Meredith probably would have played in the match if it had been a league game.
"He missed the game at Gateshead on Saturday, returned to training on Monday, but then felt his calf tighten up again.
"That might be a sign that there is a little strain in there, nothing more than three or four days (out), but no reason to risk him.
"Young Reece (Webb-Foster) has a bit of a tight hamstring and James (Hanson) pulled out of training on Monday with a little niggle.
"He just felt a little twinge in training so again, like with Mez, there is no point risking anyone at this stage of the season."