Hey,
Another form video from me - back extensions are always one of my least favorite exercises - I did the initial weeks of this on a back extension machine that didn't allow me to get to horizontal - then found a GHD and things got a lot more challenging.
Read some points on other videos about trying to keep the elbows back, make sure to look up to fully extend the necks, and try and get the chest vertical at the bottom.
Thanks again for any feedback.