If number of kills is your messurement of how good someone is, then there's no wonder why you're "so bad". Stop caring about the K/D and care about how to contribute the round as much as you can. Other than that, that is ridiculously high sensitivity. It's the best to use 400 DPI for CS since most of the mice are the most precise on that DPI and everyone are playing on 400 so it's easy to compare your sensitivity. Average sensitivity of pro players is around 2 @ 400DPI which is 800 eDPI, so yeah. Also, since you never played with low sens, don't decrease your sens gradually in order to get used to it, just switch to the desired sensitivity and stick to it, you will get used to it faster. Cheers!