There should be a PIC SIZE button on your tv remote to change aspect ratio from wide to 4:3…

As the other guy mentioned you may want to try to set the aspect ratio of the tv to 4:3.
It might not be that noticeable to you but the 4:3 image is stretched to 16:9.

Here is comparison images of the difference with stretching 4:3 to 16:9
https://imgur.com/a/699ERbs

We used to do this while singing "Head and shoulders, knees and toes, knees and toes..."

I was 17 when the N64 came out ;)

Got my copy of Mario 64 and my N64 all hooked up and working. Felt like celebrating.