In case you are ready for a lengthy explanation of what Ski_Dad and Clydesdale already have pointed out in short: You are encountering the most common problem of beginners - the feet are too far from the butt, thus your center of mass is too far back (not above, but behind your feet) from the very beginning. In order to stand up the easy way, we need to extend our legs “downwards” - in a 90 degrees angle to the planing skis.If our mass is behind the feet, we can only extend our legs forwards (not downwards) which does not do anything to help us rise from the planing skis- it only leads to the skis slipping out in front of us while our butt is dragging in the water. In other words:in order to extend our legs, we have to push the feet away from the body.If the feet are in front of the body, we can only push forwards.We need to have our body directly above the feet to push the feet downwards – this enables us to stand up the easiest way. Standing up sooner, as recommended in the guide, (before the skis are in a vertical plane) - is the method used by more proficient skiers: it requires (and allows) pushing the feet forward (in a 90 degrees angle to the rather upright, not yet planing skis).This approach requires higher amounts of strength and body tension (because you are creating more pressure pushing your legs against the boat's pull) and balance (because your center of mass will already be elevated while getting onto plane). In preparation for the start procedure on dry land you shall practice to SQUAT - not to sit!Be aware: the squatting position is quite a challenge for most grown-ups - but obviously you got some months to practice till your next attempts... In the water you must focus to have your ankles bent (while having the ski tips out of the water), your heels against your butt, your knees against your chest - as in a squat! - and your arms around your knees. Be patient: let the boat do the work, have the skis get on plane and ski with your center of mass directly above your feet - as in a squat - for several seconds before slowly extending your legs.