This is called toe-in, and is purposely built into the vise. It's a sign that you've installed the Crisscross correctly. Toe-in ensures that the vise closes first at the top. This allows the vise to hold firmly. The gap at the bottom can be about 1/8"-1/2" depending on your chop height and how you installed the Crisscross. The distance is not important as long as your vise works properly and holds well. See the installation instructions for more details. Read more here.