The Freedom Flight design doesn't have much dihedral does it. Sometimes increasing dihedral a little can get the span under limit if you are close, but not with a flat, or nearly flat wing. Too much dihedral change needed to affect span.
Here's how I'd attempt it.
First, make sure you are fresh and relaxed, this is going to be finicky, don't wait till the contest or you'll be VERY sorry. Make sure you have a good place to work.
OK, ready to start.
Carefully cut off the tip plate. If real solid, consider doing this when you cut off the outer rib later (below). If you used balsa cement, consider dissolving it off. I wouldn't use debonder if you glue with CA.
Make an extra rib, make sure it fits snugly between the spars at one outer rib. Coat the top with your favorite covering stickum and glue it just inside the outermost rib. Leave just enough space between the two ribs to slip an knife between to cut off the outer rib. I'd use balsa cement on ends of the rib to glue to spar to prevent gluing the new rib to the old. Let it dry VERY well, overnight if possible.
Carefully cut off that outer rib with a real sharp knife.
Re-attach the tip plate.
This may all fail, be prepared mentally to make a new wing. Heck, you may want to make a new wing FIRST as a security blanket. Probably easier.
And don't worry! If you are winning contests like Solon at 2:45 plus, you can do it again if you build a new wing carefully.