The choice is yours, of course, but I would cut the extra half inch off. It's just part of paying attention to the details.

My preferred way to cut a blank is with a Dremel tool and one of the little cutoff wheels. Quick and smooth with very little chance to damage the blank. It can also be done with a razor saw (from X-Acto). This has a bit more chance to damage things but works fine if you take it slow and easy. One last way to get the job done is with a triangular file. Use one of the points and file a groove around the blank. Keep filing until you separate the pieces Time consuming but it works.