One of my biggest "sighs" is when you are Embossing a card whether its with Vellum or On Whisper White CS, the edges sometimes start to curl, or the piece of CS or Vellum you are using starts to bend. Never a good look when you are trying to make a card.
Here's an easy tip:
When getting ready to emboss a card. Attach the CS to a Clipboard that has Aluminum foil (tinfoil as we call it) to the back of it. Then emboss your card. The "tinfoil" will draw the heat away from your card and you won't have any curled edges or bent CS.
I just use some two sided tape to adhere it to the back: