If you have a spare piece of the cushion fabric, you can cut a piece about 1" bigger all round than the hole.Carefully trim any burnt edges off the burn mark first. Purchase some iron on interfacing (from a fabric shop, or use iron on webbing for hems ) and iron on (using a damp cloth- say a cotton handerchief) the interfacing all around the patch EXCEPT FOR THE SIZE OF THE HOLE and then peel off the interfacing (not applicable if you have used hem webbing) and after placing the fabric, right side up, behind the hole,use a damp cloth again to iron patch to the cushion.
Julia
November 2010