Timing for awarding a DFK after Advantage doesn't develope

I would love some feedback on a situation I ran into in my last game.

In a U12 game, we had a very effective counter attack leading to a lone attacker dribbling down the first, straight towards the goal in the dead center of the field. Just one defender was in position to challenge and the keeper was in the goalie area.

The Attacker was faster and was a step ahead of the Defender and as they approached the penalty area (about a yard out), the Defender tugs on the Attacker's shoulder. It wasn't egregious, but it did twist her body a bit and it allowed the Defender to catch up. I held my whistle to see if there was Advantage. The Attacker got two or so more touches, but it was basically 50-50 with the Defender continuing to challenge shoulder to shoulder. Just outside the goal area, the Attacker got off a very weak kick that looked more like a dribble than a shot that the keeper easily stopped (maybe about 3 or 4 seconds after the foul). At this point, I blew the whistle and awarded the DFK just outside of the penalty area where the foul occurred because in my judgement there was no Advantage. The Attacker took the kick and blasted it a goal.

Defender's coach didn't say anything about it at the moment, but after the match he asked for a clarification on that play, which I walked through. He was polite, but he felt that I called it wrong and I effectively gave the attacker two chances: either I should've called advantage immediately and let the play stand or I should've blown the whistle right away. I agree the timing was awkward, but I felt it was important to hold the whistle. If a whistle was blown and I had been the attacker or the attacker's coach, I know I would've been pissed in case there was Advantage.

Of course no one else was there, but based on my description, should I have handled it differently?