Change url

I have a post i created and the url is as follows
Websitename.com/my-keyword-and-didint-realise-my-url-post-was-this-long/

It got indexed and didn't rank in top 100, so I decided to do a bit more on page seo, but also want to change the url name to

Websitename.com/my-keyword/

Do I have to do a 301 redirect or should I not worry?

you should 301 it to the new URL in order to avoid having 404 pages on your site as this can affect your (future) rankings

Yes I would 301 the old url to the new url.