Inadvertent Whistle Question

[Vinski]

Had one myself the other night. I was lead and watching off ball post play. Player B1 ended up alone in the key and for some reason I started a three second count on him in my head. Well, at 3 seconds I blew my whistle. But just before I signaled I realized that this was a defensive player. I called an inadvertent and gave the ball back to team A. Fortunately, the offense wasn’t making a move to the basket.