Game ending err

[loners4me]

2 man crew....3 seconds left in the game, team A down by one. Endline throw-in in As frontcourt. Spot throw in. Im trail. Partner tells kid he can run endline. He takes 3 steps to the left, hit A2 cutting in the lane who made the layup and horn sounds. A1 celebrating. B's coach irate since A moved on a spot throw in. I talk to partner who said " my bad, what do we do now?". B's coach says regardless of partners mistake its still a violation. A's coach says you cant tell my kid he can.run the endline and then penalize him when he does. Partner left it up to me to correct.

I waived off the basket, gave it back to A1 for a spot throwin and put time back.on the clock. They failed to score. Team B won.

Was I right? Wrong?