Can't offer much more detailed advice than keep practicing, like Ellipsism said. Video of your bowling would help though, there might be some things you could change with your action that will improve your accuracy.
Too many of my leg breaks used to land too far outside off stump and it wasn't until I stumbled across a Stuart MacGill video during a late night binge of youtube bowling technique videos that I realised my back foot wasn't aligned correctly. It was a really tiny thing that ended up making quite a big difference.