SonnyWimps: I would like to make a correction, leaning forward wouldn't be the correct way, even if it helped. You must always stay back in transitions.. :)
My advice is to shorten the reins, lean back, stay in a circle or at a corner, then turn the horses head to the outside (towards the fence/wall), put our outside leg (the one by the fence/wall) back and inside leg forward right behind the girth or even on the girth, and squeeze/kick.
There's millions of ways of fixing this problem, it really all depends on the horse. It would be easier for me to see a video where you attempt this, but as I read in an earlier comment, you don't have a video, so I guess you'll just have to try figuring it out, we can only give you small advice. :)
"When I bestride him, I soar, I am a hawk: he trots the air; the earth sings when he touches it; the basest horn of his hoof is more musical than the pipe of Hermes." -Shakespeare