clinker/hit a clinker

Before I Say Good-Byeを読んでいます。ボートの爆発事故を近くにいた船上から目撃した少年は事故後にその時のショックで様子がおかしくなり、ボートから蛇が飛び降りたなどとも言っています。少年は精神科の医者に診てもらうことになりました。
Dr. Megan surprised him, though. She didn’t seem to want to talk about the snake. She asked him about school, and he told her he was in the third grade. And then she asked about sports, and he told her he liked wrestling best, and he told her how the other day he won his match because he pinned the other kid in thirty seconds. Then they talked about music class, and he said he knew he didn’t practice enough, and he told her that he hit a real clinker when he was playing the recorder today.
リコーダを演奏している時に "hit a real clinker" とは何でしょうか？　"clinker" を辞書で見ます。
・Oxford English Dictionary: A wrong musical note.: Suddenly, I hit an obvious clinker with my right hand - a wrong note that had never happened before and that sounded pretty stupid.
・American Heritage Dictionary: A sour note in a musical performance: hit a clinker.
動詞は ""hit" が使われるようなので、"hit a clinker" で覚えると良さそうだ。