They could have named it for a reason which may not apply very well to your reason It's not a name I would choose, unless maybe I was a chemist or maybe I had cancer, something related to my life - but neither of those are so it's a very personal name.
Find a theme you like and get a name that way. I actually started naming my female bettas after characters in greek mythology.
Not offensive, but it is an odd name. It's short for chemotherapy for most. I'm not sure why you would name a betta that? If you didn't mean that then you could just say it's Kemo and you made it up and that's fine, otherwise I'm not sure why it would be named Chemo.