What always helps me is move your feet BACK about 3-4 inches. Do not move left or right just move your whole stance back. Hope this helps but it hink it wll cuz i just got home from bowling and i was in the pocket everytime and then i moved back and it helped.
Its like this, If you keeping leaving 10 pins and 7 pins, it means your either coming up light and the 6 isn't taking out the 10 pin. with the 7 pin, if you hit the pocket just right and you see the 4 pin go right in front of it, it may have been a liitle high. If you play a line that will get your ball dead in the pocket every time without leaving a 10 or 7 pin, you should be just fine. Just keep practicing. All you need to do is adjust a little and you'll be ok.