Your swing is too up-and-down, which causes either a fat shot or a wild slice.
A too-steep backswing creates two problems:
1) The resulting steep downswing will force you to stick the club in the ground before impact (fat), and
2) When you take the club back too high, your forearms tend to rotate down, cupping your left wrist and opening the clubface (slice). To swing the club properly around your body, think about keeping your elbows level at the top.
Here’s a good way to learn how to keep your swing on plane. Take the club back and find your position at the top. Then, have a friend grab another club from your bag — something long like your driver or 3- wood — and try to balance it between your arms (see photo).
If your elbows aren’t level, the club won’t be straight. Practice this until you can feel the correct position all the time.