Middle Grade or YA?

Yesterday I began working more on my diary sequel. As you may have seen on my blog in the past year, I have received feedback from several people whom I have let read my story. Only one gave a bad review and one I have not yet heard from. But everyone else who has read my story has given me good feedback. 

I have now wondered how to classify my novel, whether as middle grade or young adult. The protagonist is 12 in the first book and is about to turn 13 in the WIP sequel. Also, the leader of my writers group said it sounds like a YA novel aimed at grades 4 to 7. And I'm more confused on how to classify my book based on what I have read in this link:

I may not be a parent, but the
info contained here is quite helpful
for my post.

Middle Grade Books: Ages: 8-11 yearsGrades: 3-6Length: 30-50K wordsCharacters: Protagonist (main character) is around the age of the reader, 8-11 years old or youngerTopics: friendship, family, the character's life and world, external conflict vs internalPoint of View: often third-person, meaning the narrator is outside the story looking inContent restrictions: no profanity, graphic violence, or sexuality permitted

Examples: Diary of a Wimpy Kid series, Sisters (by Raina Telgemeier), Harry Potter and the Sorcerer's Stone, Wonder (by R.J. Palacio)
 

Young Adult Books:  Ages: 12-18 yearsGrades: 7-12Length: 50-75K wordsCharacters: Protagonist is older, 12-18 years oldTopics: self-reflection, internal conflict vs external, analyzing life and its meaningPoint of View: often first-person, meaning the narrator is telling the story about himself or herselfContent restrictions: profanity, violence, romance and eroticism permittedExamples: The Divergent Trilogy, The Fault in Our Stars, The Hunger Games Now, these guidelines are just that—guidelines. Often the lines may be blurry in some books, which makes categorizing them difficult. If ever you are confused or concerned or want to learn more, read the book yourself to see if it's a good fit for your child. You are the best gauge, as the parent. You know best what your child can and cannot handle. 

I am now beginning to think that I have blurred the lines as suggested in the last paragraph quoted above. When the time comes, though, I will let others determine if they think it is appropriate for their child to read, and websites to determine what age range they want to file my story under. Books that could fall under either are often categorized as both on Goodreads.