Okay, I remember doing this same thing about 10 years ago. I used a corner trowel and left the first coat too heavy. Now as it dries, it's cracking in the very corner. Can I take something and scrape a notch in the crack and skim coat it again? and expect it not to crack later? I was doing one side of the corners and then the next day doing the other side using a 6 inch knife. Then I remembered having the corner trowel out in the garage. Wish I hadn't thought of it now .