Before gluing the craft foam shape onto the bottle cap, you have to flip it so that it is facing the other way.
However, if the shape is bilaterally symmetric (right and left sides are mirror images), like a heart, a smiley face, or the number 8, then you don't have to flip the shape at all.
b.) Flower - combine smaller shapes to make a more detailed stamp, like this flower stamp.
Take extra care when gluing small shapes using a glue gun, you can get burned! Apply the hot glue onto the bottle cap instead on the craft foam. Use a craft stick or any other object instead of your finger to press on the craft foam shapes.