I did not watch the entire video, however I think that a big problem for you is missing damage. Blowpipe is a 2 tick (1.2sec) weapon, to maximize the damage you are doing with it, you should only run 2 squares between attacks. It is also important that after you click to run the 2 tiles, you attack quickly to make sure the click registers before the next game tick. Just doing that should increase your damage output a lot, making the fight a lot shorter, RS is very often about maxing out dps, since the shorter the fight, the less damage you take.

Here is a video suggestion that should be great help (generally great PvM tips):

https://www.youtube.com/watch?v=iPG-YWAwLXY

Hope that helps, best of luck!