Hey, everyone is special in their own way. Never compare yourself to anyone. Now, stop focusing on the bad things about you. Think very carefully about what things you are good at or are proud of. I personally think, your mind is limiting you in terms of grades. Believe in your self man, makes a lot of difference. I used to have low self-esteem, everyone made me feel like I was rubbish. As soon as I started believing in myself, I did things I didn't think I was capable off, before.

For stress, trying doing exercise, I find it helps with everyday stress and lets you relieve emotions. Always try your best and believe in yourself man. If you do this I think you'll get very far.