Is smiling instead of laughing a sin?

Assalam Alaikum, brothers and sisters! Here's the situation: I was watching a video on how to do namaz correctly. In the video, the Sheikh was explaining how to lift his finger during namaz and his finger movements made me laugh a little, but I didn't laugh, I just smiled. Is my smile a mockery of religion or not? Is it a sin that I smiled at it or not? I am very worried about this.