That typically happens and its easy to fix just use your #11 blade as a scrapper about ninety degrees to the side of the plug an scrape only downward from the wired end of the plug toward the end of the plug and do this on both sides, not just the side you removed the indexing tab.

Now on the backside of the plug (the solid side) scrape in agine with the blade a chamfer to remove the sharp edge.

This will only take a moment or two and it works a lot better than an attempt to sand it down, Don,t forget the champher on the two back corners.

John