The kettlebell swing is not a squat with a slow front raise. It's an explosive, hip-hinge based movement. But let's say you already know that. There are still two mistakes you might be making:

1. Bringing the kettlebell below the knees on the swing. Keep it above the knees.
2. Allowing the kettlebell to "pull" you away at the top of the swing. It should be "loose" at the top, but don't let it get away from you.