Ok. So this isn't going to burn down your house or maim you. But unless you happen to have a curling or flat iron laying around you don't mind getting plastic burned into, it's probably best to skip this one. Not to mention the seal created by something like this isn't going to be the best. Ether buy something made to seal bags, or go the easy route and staple it. I've seen some really cute simple card stock topper ideas on pinterest for sealing bags:
Not only would this look better, but can be sealed with with staples or double sided tape easily. Plus it would be a lot easier than trying to seal it with a curling iron.