I have a 11 inch MBA. It's the one I got as a replacement for a previous one which has issues related to its keyboard. I am not satisfying with the new one: 1. The bottom of the screen is darker(more obvious than other machines in apple store) 2. Screen is too small. I used to do a lot of coding work, my eyes feel stressful after using it for some time... So...It's still in its 14 days period. My question is: Can I replace it with a 13 inch air without unnecessary cost? Of course, I will pay an amount of money to fill the gap of the prices between 11 inch and 13inch.