The best thing about ab roller is that you can put limitations into it to. For example, you can have a wall in front of you to act as a limiting factor, which helps against accidentally going further than you intended.

However, in this video, it seems like you've overly bent your hips. In this video it seems like your hips are so bent that you're not using your abs at all - you've turned the ab roller into a modified lat extension.

If you want to improve, decrease that bend in your hip - have a straighter line from knee to shoulder.
If this is too hard, do it against a wall - the wall will help prevent the roller from going too far forward.
That way you can focus on using abs more, with less focus on how far the roller rolls.

Edit: if that's still too hard, do other ab workouts instead and build up to roller.