Re: few questions
Well if you start with a simple cube and look at it in front view you'll see the vertices on either side of the cube. If you in vertex mode, drag a selection box to select the vertical row of vertices on the right side of the cube then scale to "0" along the "x" axis, it will flatten them to form a vertical straight collum.
along "x" axis to flatten
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If you did do this before you mirrored and still had problems, it could be because you overlooked something like making sure you snapped and optimized all of your veritces and surfaces to make sure you didn't have any overlapping or leftover sufaces.
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