My GMAT Experience: 750 (Q-51, V-40, AWA 5.5)

Congratulations for your excellent score,
750 is really good, you did better than 98 % of all test takers.
I think it was good that you set yourself a high target(780). But anyways 750 or 780 isnt changing much. You scored above average for every top program, therefore you dont have to worry at all. Some people here even say, that sometimes a 730-740-750 is better than a 780 - 790, because some people who got a 790 may tend to take the rest of the application(essays,...) not too seriously, because they already feel too confident.
I am sorry for your Kaplan Cat tests. A friend of me had the same problem. She took an Kaplan test, and got only 480 at the beginning of her preparation. It was a really shock for her, since she targeted for 650+. In my opinion a person should never take a cat test at beginning, because its often only discouraging somebody, especially if he/she is a non native speaker, or struggles with maths at beginning. He/she should first study the concepts and then doing some practice questions in og 12, before he/she takes her first cat. Furthermore in my opinion Kaplan tests tend to score your exam bit lower(~50-100 point) than the real GMAT does.
Anwyways, congratulations again and i wish you all the best for your future!!!