Redo it.

Move the hole in the siding or try to find a hood that vents straight back.

You could replace your hood with one that can be vented horizontally (i.e., to the rear) such as this Zephyr Tempest II 650 CFM 30 Inch Wide Wall Mounted Range Hood (available in several widths). You would have to make sure that venting through the existing hole would place the hood at an acceptable height above the cooktop, between 24" and 36" for this model.