It takes some practice to get the hang of it. Woodburner sealing requires a steady hand. Here's a tip: I seal only from the "back" side of the ribbon. Also, keep your burner wedge tip clean (use some steel wool if your tip gets too black, that can rub off onto the ribbon). Lighter ribbons or ribbons with a high nylon/poly content can singe if you let your burner sit on them too long. Basically you don't want to blast the ends...use a light, quick, steady touch, and then "feel" your ribbon end to make sure the ends are melted properly. It shouldn't be so visible to the eye, but you will be able to feel a properly sealed end.
It really doesn't take long to get the hang of it, keep practicing! For v-notch I start in the middle with my wedge angled properly (this is most of the game-angle of your wedge) and move to the end of the ribbon. Hope this helps! FruitsOFtheBLooM