If your chipping is inconsistent, the fix could be as simple as standing closer to the ball. This will encourage you to swing the club more straight-back, straight-through instead of on a rounded arc. A mental image that works great is to think about swinging the clubhead as if it were a Ferris wheel, straight up and down.

When you stand too far from the ball, the club starts at a flatter angle, which causes it to move quickly to the inside. An inside swing arc can be desirable on full swings, but there’s no need for it on a simple chip. With such a short swing, attacking the ball from the inside makes it difficult to hit with a descending blow, so it promotes that bad instinct of scooping the ball. How close should you stand? The first time, get close enough so it feels a little uncomfortable, like you’re crowding the ball. Then you know you’re doing it about right.

Source Golf Digest