This is going to sound very convoluted but please read the whole post before saying anything. I'm just a bit frustrated that there are some really intelligent untutored students in the grade who are topping every subject (particularly maths and sciences). I just don't know what they're doing that I'm not. Even though I do get tutored for some subjects, I acknowledge that it doesn't make everything 'fine'. I always make sure to make my own notes, find my own questions to do, do the work set at school (I know many tutored students who don't even pay attention at school) etc. Am I doing something wrong, or are those people working even harder than me (more than I realise)?
You're not necessarily doing anything wrong and so you shouldn't beat yourself up over it. Also, it doesn't mean they are working harder than you. What you have to remember is that tutoring is there to get the highest potential out of a student. So although a great tutor can get the highest potential out of their students and improve their abilities, a large part of how the student performs will be down to their ability level and own hard work in that subject.
Now to give you my perspective as a student who has consistently topped throughout high school and now my uni chem subjects. A lot of the time I get asked by my tutoring students, uni and other friends on how to get high marks or top. There's no one explanation of work harder and you will get the marks. During high school I had friends who similar to you studied more than me but ranked lower than me. So I can see where you are coming from in their perspective they probably felt a similar way. I can see how it would feel unfair as the person appears to be studying less but performing better, this is unfortunately something you can't do anything about so you shouldn't try to focus on this too much.
So rather than focusing on the other people and the amount they are studying, just be confident in your ability and study in a way that you directly focus on areas you need to improve in. Competition is healthy in that it can motivate us to improve, but sometimes we need to also remind ourselves that even if someone achieves a higher mark, it doesn't make your achievements any less.