locked out of admin/dashboard after messing up child theme

Hello. I was trying to add the sidebard functionality to my wordpress twentyseventeen theme.

I was following the steps on https://premium.wpmudev.org/blog/five-hacks-twenty-seventeen/?omtr=b&utm_expid=3606929-101._J2UGKNuQ6e7Of8gblmOTA.1&utm_referrer=https%3A%2F%2Fwww.google.co.kr%2F#sidebars

#4. Add a Custom Sidebar to Each Front Page Section and Page

I am a beginner and did not copy ALL the files EXCEPT the three files to be changed to my child theme folder. I did not create the child theme folder properly. Now I am locked out. I don’t know how to access my dashboard. I also don’t know how to FTP into my site’s folders to change the theme settings. Please help. I have Amazon hosting and using WordPress Dashboarrd to do everything. It was working well until now.