I have studs in the ceiling, but where the drywall from the ceiling is supposed to meet the drywall from the wall, I have nothing to fasten the ceiling drywall to, so it will only meet the wall drywall and hang freely.
What do you think I should do?
The simplest way would have been to screw the ceiling drywall first and then attach the drywall on the wall flush to it, to avoid a lot of joint compound between the panels.
Then it would have been easy to fit one stud against the other on the wall/ceiling.
Just as you write, you have nothing to screw the ceiling gypsum into. If you screw a stud into the wall stud (saddle on), then you can screw the ceiling into that stud.