predict_classes() returning only 0 or 1 for multiclass image classification
I got the answer so I'm posting it for future reference for others:

The 3 classes defined in 

train_directory = 'D:\D_data\Rock_Paper_Scissors\Train'
training_datgagen = ImageDataGenerator(rescale = 1./255)
training_generator = training_datgagen.flow_from_directory(
    train_directory,
    target_size = (28,28),
    class_mode = 'categorical', classes = ["Rock", "Paper" , "Scissor"])


in class_mode should be Rock , Paper , "Scissors"
those were the names of the folders i create but i made a mistake and spelled "Scissors" wrong in the code.

Thanks a lot to everyone who commented!