She has organised the parade. They have watched the rehearsals and were impressed (all passé composé). On the day of the parade they are also going to give out confetti, and the crowd is going to love it (futur proche - as it hasn't happened yet). 

She wanted to create an ambiance (imparfait, describing her mood while she was preparing the show) and now - at the time the story is set, which is after the rehearsals and before the parade - she thinks (in the present tense) that she has succeeded (passé composé). 

The differences between passé composé and imparfait can be tricky with a few nuances, but I reckon the only way to get a handle on it is with lots of practice and re-reading the various lessons about this over and over again (I know i have!). 

Thanks Paul. I appreciate the depth of your response and the insight that you have provided.

This confused me too - it wasn't immediately clear when the story was being told. By the end I realised what was going on.

For me too. I think the confusion arises with the opening words where she says "j'ai organisé"  this event, which suggests everything is already done. And indeed everything following seems to support this until the very end when she says they are going to distribute confetti, when suddenly it becomes evident that the organising must still happening because the actual event is actually in the future. 

I think you would be confused in English (or probably any other language) too. It is a messy mix of tenses, without a specific indicator, or anchor, of where on the time sequence the tale is being told, until you put it all together at the end. I guess it is realistic - the confused excited meanderings of the nervous organiser who thinks they have done a great job but is awaiting the crowd's adoration, perhaps.

And yes, thanks Paul - it was indeed a good detailed response you gave to the good question you asked!

Oui.  Pour moi aussi.  J'ai confusé pendant j'étais faire de test.