I'm deeply into my career and still don't have certainty about if the correct spelling is "cancelled" or "canceled". I could link to all the conflicting info, but won't.
Today I cancelled a meeting. And spell check rejected it. Checked numerous sources as I've done numerous times and kept as cancelled (not canceled) because it looks wrong the other way.
Spell check on this blog program didn't flag either spelling. Maybe they're both right?