Need your help with github: permission denied to my own repo

I generated a new SSH key, copied it to clipboard and pasted in on github > settings > SSH keys. I get an error that this key already exists.

Then in my terminal I did this eval “$(ssh-agent -s)” and this ssh-add ~/.ssh/id_rsa. I get a message that Identity is added.

But when I do this: it push -u origin master

I get the same error:
remote: Permission to MrsColombo/elsevier-twitter-rest-api.git denied to JuliaRietveld.
fatal: unable to access ‘https://github.com/MrsColombo/elsevier-twitter-rest-api.git/’: The requested URL returned error: 403

I’m starting to hate github. This stuff is public so why do they make it so hard?

Thank you in advance for your help.