Hey!
Well, as they say, you are destined to be the person you have decided to be. And if you are adamant about your decision to become a Journalist or a Writer, forget about your class 11 marks, and start preparing hard for the future entrance exams. Your class 11 marks and the subject problem is not a concern here. If you have passed 10+2, with minimum 55% marks, you are eligible to apply for most of the institutes offering Journalism programmes. But you must be ready to prepare very hard for the tests and during the course to complete your degree. Remember, from your graduation, you are building your profile, which will support you in your internship/placements.

Just an opinion, if you wish to be a Journalist in a print organisation, you must go for a Journalism programme rather than for a degree in Mass Communication. Although you will be taught Journalism in a Mass Comm degree as well.
Many institutes offer UG programme in Journalism and Mass Comm. Some of the details are,
1. Delhi University conducts DU DSJ in September- Offers five year integrated programme in Journalism
2. Guru Gobind Singh Indraprastha University conducts IPU CET in April- Offers Bachelors in Journalism and Mass Comm (BJMC)
3. Symbiosis International University conducts SET in May- offers BA in Mass Comm at Symbiosis Centre for Media and Communication
4. Christ University conducts Christ University BA CEP in April- Offers BA in Comm and Media
5. Amity University conducts Amity Entrance test in April- July (flexible dates)- Offers B.A. (Journalism & Mass Communication) across campuses

Regarding your next concern about the preparations and books, most of these exams have a similar structure, but the syllabus and pattern may differ from one institute to the other. Generally, it’s a two-part paper wherein the first part assess the language skills and the second part tests current affairs, general knowledge and media aptitude. Basis your scores of the test, institutes calls you for the selection rounds.

As you have already mentioned about your reading habits along with good language skills preparing for such exams must not be a problem. But you must keep practising your writing skills and develop a habit of learning new words every day. You read newspapers, start reading history books, and GK books as well. Such books are available in the market easily. You can try Success Master: Journalism and Mass Communication, Word Power made easy by Norman Lewis, and General Knowledge Digest by TMH.

You must refer to previous years sample papers of the test (if available on the website of the institute you are applying) to have an idea about the test structure and types of questions to expect in the test. Prepare well and you must succeed!