The answer is very simple!
The Red Sea corner pieces actually have a groove molded into the plastic corner that allows you to snap off the outside corner. Typically this is done to give you room to route a power cord for a powerhead or other equipment out of your tank, but you can use it for this purpose too.
Just grab a pair of pliers, grip the outside corner of the plastic connector, and snap it off!
your mesh top will now fit!