Sheet rock repair tonight

The angled wall on the west sloped wall in the north room has a couple issues as you can see from the photo below.

This original sheet does not meet the wood below, nor does it meet the ceiling sheet rock. The right hand side has no beam behind it for support and so it moves in and out.

I picked up an extra length of corner bead and am going to screw it to that existing panel and the wall which should secure it. 

Then the longer new sheet will cover the entire area. This will leave taping and painting.