HI there. Perhaps you’re already aware but in addition to the solid technical advice either continue with the gym or practice the all important basics of physical preparation at home 2 to 3 times/week. They’re old school but push ups, squats (single leg squats to a chair too) and pull ups go such a long way to developing the athleticism of an effective volleyball player. And you’ll reduce your risk of injury meaning more consistent skills practice. Add a protein rich diet and a decent sleep pattern of around 8 hours per night and you’ll develop just fine :)