The fact that they are not real and made up from paper causes light reflection. However this is not the case with natural flower where light is absorbed and you get very nice clicks.^^ I am actually pretty poor in PP skills.
However your PP skills are fine. Your photos look quite natural.
In the last photo however the white flower has blown highlights. White flowers have a tendency to be blown quite easily and you should check if the original photo had blown highlights. If no then you can reprocess the photo but if the highlights are blown in the original then nothing can be done except retaking the shot.
^ As the object on glass?