How to Fill an Uneven Edge of Drywall

Apply drywall mud or joint compound on the uneven area. Use a putty knife or a drywall knife and start with a thin coat. Use a sweeping motion and even pressure to apply the mud. This will help you avoid creating holes in the mud as you work. Build up the first layer and make sure it is even.

Apply more mud. Build up the area until it feels just about level to your hand. Let the mud set up according to the package directions (set time can vary widely based on the brand you're using).

Sand out the mud. Use a fine grade of sandpaper and smooth out any rough edges in your built-up area. It should feel smooth to the touch.

Use a level. Place a level over the area. If it is not yet level, apply another thin coat of mud and sand it. If it's slightly higher than the other edge, sand it down until it does read as level. This can be the frustrating part of this job, but you need a level wall. Keep going until you get the level reading you need.