Alright, I have some steps you can take that should get this resolved.
(In all the instructions below, tick marks ( ` ) indicate what to type. You don't need to type the ` characters.)
First, move the file somewhere easy to get to on your computer, like your home folder.
Shut down your computer, and then while turning it on, hold command + r to boot into recovery mode (Instructions here: https://support.apple.com/en-us/HT201314)
Hold down Command-R or one of the other macOS Recovery key combinations on your keyboard immediately after pressing the power button to turn on your Mac, or immediately after your Mac begins to restart. Continue holding until you see the Apple logo or a spinning globe. Startup is complete when you see the utilities window:
When you reach the recovery page, in the Utilities menu select terminal.
Type `diskutil list`
Find the disk that is your computer's main hard drive. On most Macs, it is called Macintosh HD. Here is part of the output from my computer. Yours may look different, but the important thing is the Macintosh HD.
/dev/disk1 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +1.0 TB disk1
Physical Store disk0s2
1: APFS Volume Macintosh HD 524.9 GB disk1s1
2: APFS Volume Preboot 76.9 MB disk1s2
3: APFS Volume Recovery 1.0 GB disk1s3
4: APFS Volume VM 1.1 GB disk1s4
The identifier for the volume Macintosh HD in this example is `disk1s1`. I will use <identifier> as a placeholder in the subsequent instructions.
Type `diskutil mount <identifier>`
(If you receive a message saying that it may be locked, use the command it gives you, adding <identifier> to the end as in the above command.)
After it has mounted:
Type `cd /Volumes`
Type `ls`
You should see the name of your disk (Macintosh HD) along with one or two other things.
Type `cd "Macintosh HD"` (replace Macintosh HD with the name of your disk if it's different). Make sure to include the quotes.
At this point you are now in your hard drive. You can use `ls` to see what's in the current directory and `cd "<folder name>"` to navigate to the location of the file. Use `cd ..` (two periods) to navigate back up to the previous folder.
For example, if you left the file in your home directory, you would type:
`cd "Users"`
`cd "<your username>"`
You can use `ls` at any point to see what's available.
Use the command `rm -rf "<filename>"` as before, once you have reached the folder where it is located. Verify you have found it by using `ls` to see that it is there. Be careful as it will delete anything you tell it to.
When finished, close the terminal window and use the Apple menu to restart.
I hope these instructions are clear, let me know if I need to explain something better.