try a different stance. most people automatically start with their right foot pointing at 9 or 10 o'clock. stand upright, not leaning forward, with your right foot pointing at 12 o'clock, left at 10 o'clock. your big toe needs to be pointing at the bull. it's weird getting used to a new stance but it's worth a try. if it doesn't work try a different weight of darts.
oh. one more thing.go throw now for ten minutes, but CONCENTRATE really hard on each dart. if that helps, you need to just work at extending the time you can concentrate for. not as easy as it sounds