Hilariously my blog (kn100.me) also got 38 percent and the site provides screenshots of other sites with similar scores, which were all 404/500 error pages... I thought my blog looked nice :(
Using my somewhat powerful but also flawed neuro net trained on over 20 years of intensive web usage gives your blog design a thumbs up. One suggestion is adding padding-top: 1em to the "Posts" heading to make it more clearly separated from the quick summary above it and more clearly related to the content below it.