Based on the screenshot and your comments, it seems you have commited in your master branch. You should create a new branch for the pull request. I don't know how to do that with an UI cliente but from the console you should do something like:
1. Clone your repo
git clone <url>
2. Checkout the dev branch
git checkout dev
3. Create a branch for the pull request
git checkout -b whatever-name-you-want
4. Modify the files
5. Add the files
git add .
6. Commit the files
7. Push the new branch to your repo
git push -u origin whatever-name-you-want
8. Go to GitHub and you'll see the pull request button there. Then just choose the dev branch from the q2a repo and the whatever-name-you-want from your repo
That's it (unless I have missed a step).