Hey @juliandrea,
You're right that you shouldn't need to add the script to your head. The @nuxtjs/prismic module handles that for you. (Documentation here.) Try removing the script from the head, and ensuring that your prismic module is configured correctly (documentation here).
Then, if you're still having issues, try the troubleshooting steps listed here.
I'll be out of the office next week, but if you have more questions, my colleague @Fares will be happy to help 
Best,
Sam