Yeah just use a bit of bonding if the gaps big.Okay mate so shall I just bond it straight than? Bring the bonding down and feather onto plasterboard?
Don't forget to scrim it either way.
Then just get lid on.
Then ping a line across and use duck/duct/cloth tape above the line
Feather wall skim into the tape
Remove once done.
If your not competent enough to get a straight line freehand which is difficult it's the easiest way to get a straight line.
Don't lather it on at the tape otherwise you'll get a Ridge. Make sure you feather it into the tape.
It will look bob on when done