There are two ways to "fix" it:
1. Ignore it. Really - it's not hurting anything. You can just turn off the column that shows whether it's matched or uploaded, and you won't see it anymore.
2. If these are songs that you purchased from iTunes, you can delete your current track (make sure you check the option to delete from the cloud too, and obviously make sure you have a backup copy just in case something goes wrong) then go to the iTunes store, into the "purchased" section, and redownload the purchase. The newly downloaded version will then match. (But do not try to jump between AppleIDs - you'll end up locked out for 90 days).
For songs that you did not buy from Apple, the only option is to ignore it. Matching is imprecise, Apple can only compare against what's currently in their store and that may have been re-digitized or reprocessed in some subtle way that means it's no longer the exact same edition of the song that you have - even though to your ears and eyes they are identical.
Thanks for the reply. Part of the issue is that the songs that aren't matching are indeed protected AAC files and are only 128kbps and I'd love to be able to re-download them as 256kbps. Ironically, it's almost entirely purchased songs that are doing this, so the minute differences don't exist and if they are indeed different, I should be uploading them anyways. I did fall into the 90 day trap after reading that I wouldn't be able to auto-download for 90 days, only to find that I was locked out of match altogether. Horrible buggy system and now I'm out three months of my year of service because I dared to have songs (not the songs in question) attached to an old Apple ID!