I created a new barebones theme that is inheriting from antimatter and i wanted to modify the base.html.twig file so that i could change the footer text. maybe i am missing something. i followed every step in the create a new theme tutorial.
Just a few ideas…
Have you selected the right theme? 
Caching is off?
If you have created a new theme you can just edit the theme in /user/themes/[yourtheme]/templates/partials/
Everything you edit there will be taken over by the theme. 0