I think it's brave that you're coming back to school and giving it a go despite missing an entire year of school. I remember when I got sick with a manic episode and I didn't get the grades for the university pathway I wanted. I remember how I used to tell myself that I wouldn't make it into university. In my final year of schooling, I was not where I wanted to be because of my sickness. So I went back to school get the grades I needed to go university.
I think with school, it's important to have a study routine and to be disciplined. Don't do your assignments last minute, plan for them ahead. If you have questions, ask your teacher in private. If you're not coping, ask for help from the school counsellor or from Kidshelpline or from your friends.
Honestly, you're not a failure, you have your whole life ahead of you. You'll work hard to get to where you want to be. Work for your future.
What matters is your progress, you're trying to do better yourself not compete with other people. I guess you feel inferior to other people. Don't. And I've also disappointed my family with my sickness and grades.
Hope this helps?