When you get a grip on the platforms as marked, you will be well on your way. When you pop the first flake off, if it is short, you have placed too much pressure perpendicular to the flake path and not enough pressure in exactly the direction you want the flake to travel. Watch closely and determine whether the preform is twisting in your hand when the pressure begins building up. It takes a lot of strength to do good pressure flaking, and can take a lot of practice to develop that strength. A lot of pressure flakers complain about sore hands, wrists, forearms, elbows and even shoulders when they are in the first few months of knapping. Don't feel bad about asking questions. We all have asked, and we all have been where you are.
WA