Without even looking at your description, I noticed a slow shutter speed and the "plastic" skin.
Yes, f/2.8 is definitely way too small for HS gyms. The 1.8 lets in more light, which = more shutter speed = more sharpness. Or, if there's alot of light (some HS gyms have windows), you could take a step down to ISO 800 for less grain. I've never been able to get over f/2.5 in a gym, and even that was with better than average lighting. The 1.8 is also lightning fast in the autofocus. It's regarded as the ideal lens for volleyball and basketball.
I usually shoot RAW - it's so much more forgiving for mistakes and much easier to batch process. I usually do not shoot bursts in volleyball (except maybe for serves).
One tip that I have found useful is to use the "M" mode since the light usually does not change much. Aperture should be max (but the 1.8 loses some sharpness there, regaining it by 2/3 stop smaller), ISO 1600, and get the max shutter speed you can while keeping the exposure between 0 and 1. I usually accept 1/500 as a minimum shutter speed. And even though it's minimum, going higher won't really do much more. Once you have achieved 1/500, you can open up the aperture a couple of 1/3 stops, and maybe look at lowering the ISO.
At the home gym, I usually set my camera to 1/500, 2.2, ISO 1600 - the gym's just bright enough.