Hello, I made this pretendo network ID for my 3DS, and I chose the username I have right now because I always use it. But when I went to link my account to my 3DS, it said my username was already used. The only thing I could do is to delete this PNID and create a new one, but I cannot find an option to do it.
Correct; your PNID cannot be the same as the NNID.
I have forwarded the request for deletion.
BTW, it’s recommended to make your PNID directly on the console! 
The account deletion has been fully processed.