Consider approaching the execution of the large cross stitch in this way:
What is different here? Well, look at a stitched sample:
Cross Stitch Executed in a Chevron Style
This is indeed a cross stitch shape, but the execution is a zig zag stitch or Chevron pattern. The nice thing about this form of execution is that you do not see any travel threads that are on the back of the piece because it is executed with backstitches. This is what the back looks like:
Backside of Cross Stitch Executed in a Chevron Style - All Backstitches
The question that you need to ask yourself is whether this type of execution is a problem. Do you want a crossed stitch or do you want a cross stitch shape?
Many times the large cross stitch is used with the center area stitched over with another decorative stitch, which hides whether the stitch is really crossed or not. Here is an example with an upright cross stitch:
The Upright Cross Stitches Hide the Intersection of the Backstitches at Center of Cross Shape
Oops! See what is visible here? A travel thread from upper right to lower left, however, the travel thread from upper left to lower right is well hidden.
Here is the backside:
Backside of Cross Stitch with Intersections Covered
Hiding that travel thread that shows through to the front would not be hard - just whip the red thread to the line of metallic threads on the back using a piece of sewing thread or one strand of cotton floss the same color as the canvas.
Consider using this form of stitching when you are working a laid filling pattern with diagonals in both directions. These types of patterns most often have that middle “crossed” intersection covered by a decorative stitch. Many stitchers find that compensating these laid patterns difficult, especially when the area covered by the stitch is not square. There is no shame in stitching the pattern this way - it is simply a variation, or a “faux” cross stitch or “faux” diagonal laid filling pattern. I teach laid fillings this way all the time. I don’t want anyone to get so hung up on counting on the diagonal that they miss the fun of working the stitches.