WordPress uses index.php to display your Blog Page or Archives page and hence they will always call for excerpt.(Unless it is modified otherwise).
Now, single post or articles will be calling the content-function displaying the full content.Follow the below steps :-
Step 1 :- Open your single.php and check for
<?php the_excerpt(); ?>
Step 2 :- Replace above code with :-
<?php the_content(); ?>
This will change single posts to show all content in your case.If you have content-{post-format}.php then you will need to change them too.Hope this helps. 🙂