Missed Mini Windmill

This is a showdown between Caleb and James. Caleb would go on to win the game comfortably but there is a huge missed opportunity here by implementing the concept of windmills. Windmills are when you use a perpetual check to remove several of your opponents pieces. It often involves bishops and another minor piece, like a rook or knight. Go to move 11.  First, explain why knight to a7 was a blunder. Second, see if you can find a way to guarantee James loses his queen in three moves from this position.