Kal Naismith's first goal for the Gers helped them edge through against their Highland League opponents in the third round on Saturday.
"It was a relief because we weren't good today," McCoist told reporters. "As much as I'm happy to be in the next round, I don't think I would be doing my job if I didn't register my disappointment at the way we played and passed the ball.
"We are through, we are in the next round and that was the object of the exercise but we will have to have a wee chat."
Rangers continue their Scottish Third Division campaign on Saturday whey then travel to Stirling Albion.