As-salamu 'Aleykum!
Oh, Subhanallah ukhty. I'm saddened to hear this too. But, Alhamdulillahi-ladhii bi ni'matihii tanimma-saalihaaat!! What happened was bound to happen, and as you said, instead you learn from it and move on.
But I have a feeling smething was not right about you guys' flyers? You know sometimes, people just get attracted by them and attend the event mostly because of how the flyers look. I know of many lectures that many haven't attende because the flyers looked somewhat bold.
So Insh'allah, when next time you plan on re-doing the event(I agree with wat the sis^ said, yu'll do this Again because you're strong and you don't let people discourage you

), just keep that in mind.
May Allah swt reward you two, and the sheikh, for your great efforts in trying to spread this deen.Aameen.