Hi! Congrats, you are soo close! Note that you don't need modify master (and it's not allowed, you will get disqualified if you do so...), so any change you do, do it in a new branch you create.
Whenever you finish your job, clean the repo removing the branch you created (and any other log that you might have created):
To remove a branch:
git push origin -d <branch-name> #remove remote branch
git branch -D <branch-name> #remove local branch