Passing a School Bus - Wa

I was recently next to a school bus on a two lane street. The yellow lights were flashing so I was driving slowly, anticipating the stop sign to extend. However, when it did, by the time I reacted and came to a stop, I was already in front on the bus, so I drove away after stopping. I got a ticket with the video/picture.

Do I have any legal defense here, either to contest or explain circumstances? I’d appreciate your input!

Passing a School Bus - Wa