Feel guilty/not good and smart enough for grammar schools.

I always try push myself to work my hardest and get the best grades. I currently go to a normal academy and i get one of the best grades in my year group and im in all top sets. However i still feel like im not good enough compared to granmar school students and that even if i get high grades at my school its still not good enough to be classed as 'smart'. In a way im jealous of grammar school students because i feel dumb and hopeless by them as i wont be as successful which hurts a lot. It is important to me as i do want to apply for a sixth form at a grammar school.I just need some advice to help with this feeling. My current grades are:
7+ biology
B+ business
7 chemistry
6- english language
6+ english literature
7+ geograohy
6+ maths
6+ pe
7 physics
A sociology
5 spanish
I am moving into year 11 this term. It is also more stressful for me as i really want to study medicine and that requires high grades.