I lay them down in separate steps. First layer of petals, implode, stamen, implode, second layer of petals, implode, leaves, implode. Each step I only push it on the marver gently once or maybe twice before the next step. Also, be sure to keep the top glass hot so you don't flatten it when you are pushing it in. HTH
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ETA: I forgot to add that in my pendants I've found that adding the leaves at the same time as the second petal layer makes them a bit more visible but on marbles I usually do them in a separate step. Also wanted to add that I learned how to make flowers from a class with Sabina Boehm. She's fantastic and worth every penny if she teaches near you!