It sounds like you are letting your horse turn too soon (cutting the barrel close), and then for your horse to avoid hitting the barrel, she has to make the end of her turn wide to get around it. Dont' let her turn too soon! YOu should be in control of her at all times using your legs, seat, and body , with the reins as your "last resort" cue. And never tip your horse's nose away from the barrel to avoid turning too soon. That just makes them shoulder-in to the barrel and you lose the natural arch in the horse's body to complete the turn properly. Instead, use your inside leg to push the horse over and awway from the barrel.
There was just an article about this in Barrel Horse News by Dena Kirkpatrick. Horses cannot see directly in front of them very well. But they can see your direct rein hand, your knee, and their own hip very well (one eye at a time). So if your horse cuts that barrel too close going into the turn, the horse can't see it, the horse panics,, and goes wide because she can't see the barrel. It has become an obstacle.
Rather, make sure you are going wide enough into your pocket, approximately 4 feet from the barrel (although this size will vary for each individual horse). You also don't want to go in too wide, though. And make sure you do not turn that barrel, until it is at least behind your knee.
Here's one of Dena's videos that talks about that.
She has lots of other videos on YouTube from her DVD series. I suggest you watch them.
And if you do have a video of yourself, that would greatly help us help you!