Sure, you aren't under any obligation to read it unless it's for school, required summer reading, etc.
Make sure you return it on time to avoid late fees, keep privileges.
I can return a book back to the library I didn't find interesting, right?
Absolutely! You might ask one after the librarians to help you choose a book...just tell her/him what kind of books you're interested in reading and they'll assist you in finding one.
You can return it and choose another one replace, here in France, we usual do it in this way. If we find out some books not interesting, then we return them and choose some replacing ones.
Of course, it's your decision, I do it all the time. Unless it's against the law in your country. XD