Sorry, you probably already messed it up. Even if you get the rust off there will probably be pits.
If the rust is in the area that can be reground then get a fresh belt of the last grit you used and try that. Otherwise, it's hand work.
If you have access to a sand blaster you could blast the blade and give it an even light gray color while it removes the rust. Be sure to tape the guard and handle. Use Ren Wax on the blade after blasting...
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