Git – How to Cancel a Local Commit

My issue is I have changed a file e.g.: README, added a new line 'this for my testing line' and saved the file, then I issued the following commands:

git status

# On branch master
# Changed but not updated:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#   modified:   README
#
no changes added to commit (use "git add" and/or "git commit -a")


git add README

git commit -a -m 'To add new line to readme'

I didn't push the code to GitHub. Now I want to cancel this commit.

For this, I used

git reset --hard HEAD~1

But I lost the newly added line 'this for my testing line' from the README file.
This should not happen. I need the content to be there. Is there a way to retain the content and cancel my local commit?