Scoring 60% on Scrum.org's Scrum Open is not yet close to bring ready to take the exam for real. Although some people say that you should be able to consistently score 100% on the practice exam, I believe that consistently scoring in the upper 90s% is more than sufficient. Fortunately, there are plenty of free resources to help.
First, I'd recommend reading the Scrum Guide. Even if your native language isn't English, a common recommendation is to understand the English-language version. Not all languages are fully up-to-date and some people have reported nuances that aren't reflected well in some of the translations. Plus, the Scrum.org exams are all in English. Although it's OK to use Google Translate on the exam, it may slow you down.
Beyond the Scrum Guide, Scrum.org's Scrum Master Learning Path contains links to free videos, articles, and blog posts on the different competencies relevant to being a Scrum Master that are tested on the exam. They also recommend some books that you could buy, but the vast majority of the content here is free.
There are also specific suggested readings for the PSM I exam. Most of these are free, but there are also some books that you could buy. Some of these overlap with the items on the Scrum Master Learning Path.
As far as practice exams, I would recommend only using the exams from the source where you are planning to take the real exam. In the case of the PSM, I would only recommend the Scrum.org practice exams. They keep the practice exams up-to-date with the latest version of the Scrum Guide and their exams. Other practice exams may be of differing levels of quality and the way the author interprets the Scrum Guide may not be consistent with Scrum.org - an answer deemed to be correct on a different practice exam may be considered wrong by Scrum.org.
