Can forking a repo disconnect me from the main branch?

Hi all,
I am new to coding & GitHub and I am a collaborator on a repo for work. My question has 2 parts. For one, I accidentally branched the repo to my own account, and wanted to delete it, but was afraid of also deleting the main branch (since I am a collaborator on both). Can someone confirm if I navigate to the forked repo settings and click “delete repository”, it won’t delete the main branch?
In addition, I made some changes to the README.md and was able to commit, but when I pushed I got a 403 error. So, I tried creating a new test connection for the same project, and it still didn’t work and now the error is: “git@github.com: Permission denied (publickey). fatal: Could not read from remote repository. Please make sure you have the correct access rights and the repository exists.” Could this be because I forked it? Does anyone have any advice for resetting all this to normal so I can push? Any direction would be greatly appreciated.

Thank you!!