How to remove accidental files from the Jekyll _site folder

So I just recently got started with Jekyll and had no clue what I was doing. I somehow managed to get two files into the _site directory and now they are there to stay. I can delete these files, but when I run

bundle exec jekyll build

to build the site, the files are back. My question is, how can I remove these 2 files from the _site directory?
Here is a tree of the _site directory. The files I want to remove are sync.py and README.md.

.
├── 2020
│   └── 04
│       └── 24
│           └── get-system-platform-python.html
├── 404.html
├── README.md
├── about
│   └── index.html
├── assets
│   ├── css
│   │   └── style.css
│   └── images
│       ├── bkg.png
│       ├── blacktocat.png
│       ├── bullet.png
│       └── stack.png
├── favicon.ico
├── feed.xml
├── index.html
├── jekyll
│   └── update
│       └── 2020
│           └── 04
│               └── 24
│                   └── welcome-to-jekyll.html
└── sync.py

The Jekyll stuff is in this Github repo: https://github.com/noahbroyles/site-genny
I'm not sure if that helps or not because I have the _site directory in .gitignore.

Is it even possible to remove these files?
Any help is welcome!

Solution

Simply add sync.py and to README.md the exclude list in _config.yml.

exclude:
 - sync.py
 - README.md