Just keep your hands moving constantly. It takes a lot of practice to really nail down the subtle throttle and stick inputs. Even after years of doing it I am never truly "stable." I can usually refuel in a single connection, but I'm moving slightly up/down, left/right, and forward/back, and my hands are constantly making adjustments accordingly. I also recommend checking your curves and maybe adjusting them. I use the curves from Chucks A-10C guide with a TM Warthog, I would start with that to help reduce the sensitivity near the center.