For all of the good things Ryan McDonagh has done, he may have spent this whole time being underutilized. At least that’s the opinion of Rangers coach John Tortorella, who Friday admitted he has made a mistake in not playing his top-pair defenseman on the power play more often. “It’s me. I screwed that up, not using him earlier [on the power play] and I should have,” Tortorella said as his team prepared for Saturday night’s Game 5 of the Eastern Conference semifinals against the Bruins, who hold a 3-1 lead. “He wants to become that complete player, and he is still so wet behind the ears as far as his age and what he needs to learn about that position that it’s really encouraging.” McDonagh has shown sparks of offense in the playoffs, especially in the 4-3 overtime win in Game 4 on Thursday. He made a great solo rush up the ice and hit the post early in the second period, and went out with the first power-play unit for the team’s final two man-advantages of the game. The 23-year-old Minnesotan got 3:32 of the team’s 7:05 total power play time, and created momentum that led to Brian Boyle’s game-tying goal in the third period. With each kind word spoken by the coach, it’s also clear McDonagh’s stock as a restricted free agent this summer is rising. “I think that when players are deemed a shutdown defenseman, and [the emphasis is the] defensive part of it, I think sometimes players get trapped into, ‘This is what I am,’ ” Tortorella said. “Ryan McDonagh is not just that, and he’s going to be able to do both.”