I understand the situation.
It's too bad you did not check the perimeter of the room prior to starting, as it may have 'suggested' to you that you start lower and use a filler strip above that could be 'adjusted', or scribed to the ceiling as needed.
In this case you do have some small options that may make the gap less obvious.
If the ceiling tiles can be removed (if you have extras) you could shim them, starting a couple of courses away, so that the ceiling 'drops' slightly to lessen the gap.
The other option is to use a filler strip above the gap and paint it so as to shadow it from the crown molding. If that sounds confusing, I'm sorry, but I can't explain it any better.
Basically you'd be trying to 'fool the eye' with a shadow line, but it would be easier to do if you did not have such a different material on the ceiling.
Hope some of this helps somehow.