Let me tell you something, I knew 2 people who started preparing before 11th for Neet, one of them got selected with 12th nd another after taking drop. Nd both got in reputed med schools of India.
It’s a very crucial desicion that only you can make, all I can say is if you are so clear about pursuing Mbbs then there is nothing wrong in starting your preparation early, it won’t go waste, knowledge never goes to waste! But what you have to know that it’s not a necessity but simply a choice. You aim high, you work hard. But be prepared for the repetitive chapters ahead, you’ll learn nd master many, but like some droppers you may face boredom out of many topics over time, which may lead to skipping there revisions nd there’s a chain where things can go wrong or right. This education system is not perfact, but things r designed according to the amount of knowledge an average student could be or should be exposed. If you think you can handle this extra knowledge earlier, then good, otherwise school is such an awesome place, enjoy what you have now.