the search volume and KD score don't mean too much, you need to check which pages of which sites are ranking in top 10 for this keyword, that will tell you how tough ranking for this keyword is...
Nowadays, mostly big authority sites are ranking, so if your domain is weak (less than 20 DA or DR) and your competition has high authority (over 50 DA / DR) you'll need to improve the authority, and this takes time and money...
These being said, with proper SEO you might see some improvements, especially since your domain seems to be in good standing with google, which is important. Just analyze your competition's content and backlinks profile for their ranked pages and try to mimic what they're doing. Also, a few internal links with exact match anchors should help, so try to get 2-3 such links from already indexed pages (if they have traffic if it's even better) that are extremely relevant to the page you're trying to rank for this "main keyword". Sometimes this does boost the rankings a little bit...
But yeah, authority is a big deal nowadays, if your domain is weak you might want to point a lot of strong backlinks to the homepage of your domain to up its authority, otherwise...