drywall seams

Have less than a 1/2 inch shiver gap between ceiling right above shower. Tried filling the gap with mud but no success. The mud keeps cracking after application. Any suggestions. I thought about sanding it down and covering it with some simple crown molding trim. Any suggestions or improvement

Hello Everyone!! I apologize in advance if I'm posting this in the wrong forum, or if some parts of my post belong elsewhere. I'm VERY NEW to understanding the lingo of home remodeling, so I've tried to point out my areas of concern as easily as possible, without making a fool of myself haha...