Advice on ceiling joint

I’m in the process of remodeling my bathroom. Being a DIYer i am doing everything myself. I need to know if I can use a backer board between one lip of a piece of Sheetrock or if I should rip at all out and redo it. Here’s a picture thanks in advance. It’s my second time hanging drywall so don’t be too harsh.

I’m in the process of remodeling my bathroom. Being a DIYer i am doing everything myself. I need to know if I can use a backer board between one lip of a piece of Sheetrock or if I should rip at all out and redo it. Here’s a picture thanks in advance. It’s my second time hanging drywall so don’t be too harsh.