You don’t need straight As in A level to get into Stanford (but it does generally need to be high). The US admissions process is holistic. This means more parts of the application decide whether you get in, as opposed to just grades, like in the UK. Things like the low-funded school with minimal resources you go to, your strong extra-curricular activities, and your impressive awards are considered. It's not like the UK where getting AAA instead of AAA will mean you lose your place at Oxford. It’s not like the UK where competitions and extracurricular activities hold little weight compared to academics. US colleges are looking for the next CEOs - CEOs made companies, they didn't focus as much on getting As.* Students get into US colleges with ABB all the way to 5A*s. The effort you put into your leadership activities also carries weight! You’re more than just your grades. They just want you to be excellent. Holistic admissions mean if you’re excellent in an area other than grades, you’re still a person of interest to them. This can be sports, awards, or competitions. Applicants to Ivy League universities often have all boxes ticked.
When you get admitted to any American college, there are no required grades to achieve at the end of the year. You can vibe out, but do finish the year strongly as they can rescind your admission if you do poorly. Though they never ask for these end of Sixth-form/High School grades.
If you have faced any adversity, they would like to know your story.
This is university after all. You are coming here to pursue a certificate of education in high learning. The colleges in this resource are the most prestigious in the world, and you bet they are looking for the brightest, most motivated students around the globe. Ivy League applicants often have a string of A* predictions at A-level, with perfect test scores. MIT and Caltech are one level above this.
*At the same time US colleges are looking for CEOs, they also looking for the greatest academic minds, like researchers. People with top grades and test scores.
The great thing about US colleges is that you can choose your course after trying lots of classes in different fields. If you don’t know what to student yet, put ‘Undecided’. If you know you want to study Physics, and you declare that in your application, make sure to show prowess in Physics.