That script allows you to have 2 (or more, for octopussies perhaps) weapon slots (dual wield ftw) and use 2-handed weapons.
Have you read the description and configured the script?
You should be able to remove the 2nd weapon slot if you want to.
This way you will not be able to use dual wield, but you will have 1 weapon and 1 shield slot like you woud without the script.
I use this script as well, and I have configured it to be like this:
Main hand
Offhand
Shield
etc.
This way, you can have all the possibilities:
- weapon and shield
- 2h weapon
- dual wield
(and yes, I have removed the possibility of having both 2 weapons and a shield equipped

)
Just configure the script to your own preferences, but read the description first. Good luck