Please modify Stretch Pose by doing one leg at a time. Have one knee bent with the foot flat on the floor and the opposite leg extended. Switch legs halfway through. Keep your hands beneath your buttocks and really stretch in the pose. Press the crown of the head away from the navel and the toes away from the navel, so you are really lengthening in the pose. Press the lower back towards the floor. In more advanced versions of this exercise it is often taught with root lock (squeeze the rectum, sex. organ, and navel in towards the spine) applied during the exercise which, along with other benefits, helps to stimulate more internal support. You might experiment with this. If it feels to advanced do not do it for now. With these suggestions and modifications you should quickly build up strength to do the full pose.