cwrr5 is correct, do not sand the braces. You want the full strength. Carefully withdraw the braces from the wing while trying not to damage anything. If things were that tight, you should have stopped sooner. Once apart, see if the following will help. Get an old (or new) nail emery board from your wife and CAREFULLY remove a minimum amount of material from the ribs that are too tight. The problem may also be caused by a slight misalignment of the spar and spar doubler or excess glue that may have worked out of the spar/spar doubler joint.

IAW, find the cause of the problem and fix it instead of creating new problems.

Oh yeah, did I mention :slow down and think?

There is usually a better idea just waiting to be found if you will look for it.

BTW the motor looks fine from what I can see but lets wait a little before drilling any holes until we see what Ken finds in the manual. There may be something there that I don't know about. Again, no rus