Prop it up against a wall or a chair lined with a towel. Some area that you're not concerned about getting messy. Choose a size of canvas that you think you can cover with the amount of crayons you have. That was a lot quicker than blow drying, huh? If you think your glue gun is salvageable, insert a regular glue stick and work through until what comes out is clear and glue-y and no longer colored and waxy. If you aren't happy with a section of your painting, with this method it's very easy to go back and redo (or add to) an area.
أمسك لوحتك. اتركه يجف.